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• 1.
Department of Physics, Yale University, PO Box 208121, New Haven, CT 06520-8121, United States.
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Dept. of Elec. and Comp. Engineering, A.V. Williams Building, University of Maryland, College Park, MD 20742, United States.
Comment on "Possible induced enhancement of dispersion forces by cellular phones" by B. E. Sernelius, Phys. Chem. Chem. Phys., 2004, 6, 13632004In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 6, no 14, p. 3915-3918p. 1363-Article in journal (Other academic)

[No abstract available]

• 2.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
Charge storage properties of biopolymer electrodes with (sub)tropical lignins2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 45, p. 24681-24684Article in journal (Refereed)

The electrochemical and charge storage properties of different lignins inside biopolymer electrodes were studied and correlated with the chemical variations of the lignins as indicated from the nuclear magnetic resonance (NMR) spectroscopic data. The varying fractions of monolignols were found to correlate with charge storage properties. It was found that as the sinapyl to guaiacyl (S/G) ratio increased both the specific capacitance and charge capacity increased considerably. This indicates that quinones generated on S-units can contribute more to charge storage in the biopolymer electrodes.

• 3.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, The Institute of Technology.
Polaron stability in molecular semiconductors: theoretical insight into the impact of the temperature, electric field and the system dimensionality2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 14, p. 8973-8982Article in journal (Refereed)

A semi-empirical Holstein-Peierls model is used to study the temperature effects on the polaron stability in organic semiconductors at a molecular scale. The approach takes into account both intra- and intermolecular electron-lattice interactions and is aimed at describing charge transport in the system. Particularly, we present a systematic numerical investigation to characterize the influence of both temperature and electric field on the stability as well as mobility of the polaron. It is found that the parameter space for which the polaron is dynamically stable is quite limited and the variations in some of these parameters strongly depend on the temperature. The electric field can play a role in further localizing the charge causing a compression of the lattice distortions associated with the polaron, increasing thereby its stability, up to a field strength of approximately 2.0 mV angstrom(-1). Considering field strengths higher than this critical value, the polaron is annihilated spreading charge through the lattice. Furthermore, we have studied the polaron mobility as a function of the anisotropy of the system, going from a one-dimensional system via a highly anisotropic two-dimensional system to a uniform two-dimensional system. There is a clearly observed mobility edge for the polaron; it exhibits a high mobility in the one-dimensional system but as the coupling in the second dimension is turned on the polaron slows down and becomes immobile in the uniform system. The results provided by this transport mechanism are in good agreement with experimental observations and may provide guidance to improve the charge transport in organic optoelectronic devices.

• 4.
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
Synthesis of a Cu-infiltrated Zr-doped SBA-15 catalyst for CO2 hydrogenation into methanol and dimethyl ethert2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 29, p. 19139-19149Article in journal (Refereed)

A catalytically active nanoassembly comprising Cu-nanoparticles grown on integrated and active supports (large pore Zr-doped mesoporous SBA-15 silica) has been synthesized and used to promote CO2 hydrogenation. The doped mesoporous material was synthesized using a sal-gel method, in which the pore size was tuned between 11 and 15 nm while maintaining a specific surface area of about 700 m(2) g (1). The subsequent Cu nanoparticle growth was achieved by an infiltration process involving attachment of different functional groups on the external and internal surfaces of the mesoporous structure such that 7-10 nm sized Cu nanoparticles grew preferentially inside the pores. Chemisorption showed improved absorption of both CO2 and H-2 for the assembly compared to pure SBA-15 and 15% of the total CO2 was converted to methanol and dimethyl ether at 250 degrees C and 33 bar.

• 5.
University of Manchester, England.
DESY, Germany. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering. University of Manchester, England. University of Manchester, England. University of Manchester, England. University of Manchester, England. University of Manchester, England.
On the origin and variation of colors in lobster carapace2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 26, p. 16723-16732Article in journal (Refereed)

The chemical basis of the blue-black to pink-orange color change on cooking of lobster, due to thermal denaturation of an astaxanthin-protein complex, alpha-crustacyanin, in the lobster carapace, has so far been elusive. Here, we investigate the relaxation of the astaxanthin pigment from its bound enolate form to its neutral hydroxyketone form, as origin of the spectral shift, by analyzing the response of UV-vis spectra of a water-soluble 3-hydroxy-4-oxo-beta-ionone model of astaxanthin to increases in pH, and by performing extensive quantum chemical calculations over a wide range of chemical conditions. The enolization of astaxanthin is consistent with the X-ray diffraction data of beta-crustacyanin (PDB code: 1GKA) whose crystals possess the distinct blue color. We find that enolate formation is possible within the protein environment and associated with a large bathochromic shift, thus offering a cogent explanation for the blue-black color and the response to thermal denaturation and revealing the chemistry of astaxanthin upon complex formation.

• 6.
Chemnitz University of Technology, Center for Nanostructured Materials and Analytics (nanoMA), Germany.
Chemnitz University of Technology, Digital Printing and Imaging, Germany . Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology. Chemnitz University of Technology, Center for Nanostructured Materials and Analytics (nanoMA), Germany. Chemnitz University of Technology, Center for Nanostructured Materials and Analytics (nanoMA), Germany. Chemnitz University of Technology, Center for Nanostructured Materials and Analytics (nanoMA), Germany. Chemnitz University of Technology, Digital Printing and Imaging, Germany .
Inkjet printing as a tool for the patterned deposition of octadecylsiloxane monolayers on silicon oxide surfaces2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 20, p. 7494-504Article in journal (Refereed)

We present a case study about inkjet printing as a tool for molecular patterning of silicon oxide surfaces with hydrophobic functionality, mediated by n-octadecyltrichlorosilane (OTS) molecules. In contrast to state-of-the-art techniques such as micro contact printing or chemical immersion with subsequent lithography processes, piezo drop-on-demand inkjet printing does not depend on physical masters, which allows an effective direct-write patterning of rigid or flexible substrates and enables short run-lengths of the individual pattern. In this paper, we used mesithylene-based OTS inks, jetted them in droplets of 10 pL on a silicon oxide surface, evaluated the water contact angle of the patterned areas and fitted the results with Cassie's law. For inks of 2.0 mM OTS concentration, we found that effective area coverages of 38% can be obtained. Our results hence show that contact times of the order of hundred milliseconds are sufficient to form a pattern of regions with OTS molecules adsorbed to the surface, representing at least a fragmented, inhomogeneous self-assembled OTS monolayer (OTS-SAM).

• 7.
University of Liverpool, UK.
University of Basel, Switzerland. University of Liverpool, UK. University of Basel, Switzerland. University of Basel, Switzerland. University of Heidelberg, Germany. Paul-Scherrer-Institute, Villigen, Switzerland. University of Basel, Switzerland. University of Liverpool, UK.
STM fingerprint of molecule-adatom interactions in a self-assembled metal-organic surface coordination network on Cu(111)2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, p. 8815-8821Article in journal (Refereed)

A novel approach of identifying metal atoms within a metal-organic surface coordination network using scanning tunnelling microscopy (STM) is presented. The Cu adatoms coordinated in the porous surface network of 1,3,8,10-tetraazaperopyrene (TAPP) molecules on a Cu(111) surface give rise to a characteristic electronic resonance in STM experiments. Using density functional theory calculations, we provide strong evidence that this resonance is a fingerprint of the interaction between the molecules and the Cu adatoms. We also show that the bonding of the Cu adatoms to the organic exodentate ligands is characterised by both the mixing of the nitrogen lone-pair orbitals of TAPP with states on the Cu adatoms and the partial filling of the lowest unoccupied molecular orbital (LUMO) of the TAPP molecule. Furthermore, the key interactions determining the surface unit cell of the network are discussed.

• 8.
Univ Venice, Dipartimento Chim, I-30123 Venice, Italy Univ Padua, Dipartimento Chim Fis, I-35131 Padua, Italy Linkoping Univ, Dept Chem Phys, S-58183 Linkoping, Sweden Hiroshima Univ, Dept Appl Chem, Fac Engn, Higashihiroshima 7398527, Japan Univ Modena, Dipartimento Chim, I-41100 Modena, Italy.
EPR of trans-stilbene radical cations formed in zeolite cavities: a new approach to study the zeolite void space2000In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 2, no 20, p. 4823-4828Article in journal (Refereed)

trans-Stilbene was adsorbed in the cavities of H-ZSM-5, H-MOR and H-BEA zeolites, originating monomeric and dimeric radical cations that were studied by EPR spectroscopy. The H-BEA samples were pretreated at three progressively higher temperatures. Simulation of the spectra allowed the evaluation of the relative amounts of monomers and dimers. The nature, quantity and relative amount of monomeric and dimeric radical species were correlated to chemical and dimensional modifications of zeolite channels caused by the dealumination of the zeolite structure and extra-framework aluminium species formation.

• 9.
Uppsala University, Sweden.
University of Siena, Italy.
Which factors determine the acidity of the phytochromobilin chromophore of plant phytochrome?2008In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 10, no 18, p. 2528-2537Article in journal (Refereed)

Quantum chemical calculations aimed at identifying the factors controlling the acidity of phytochromobilin, the tetrapyrrole chromophore of the plant photoreceptor phytochrome, are reported. Phytochrome is converted from an inactive (Pr) to an active form (Pfr) through a series of events initiated by a Z $\rightarrow$ E photoisomerization of phytochromobilin, forming the Lumi-R intermediate, and much controversy exists as to whether the protonation state of the chromophore (cationic in Pr with all nitrogens protonated) changes during the photoactivation. Here, relative ground (S0) and excited-state (S1) pKas of all four pyrrole moieties of phytochromobilin in all 64 possible configurations with respect to the three methine bridges are calculated in a protein-like environment, using a recently benchmarked level of theory. Accordingly, the relationships between acidity and chromophore geometry and charge distribution, hydrogen bonding, and light absorption are investigated in some detail, and discussed in terms of possible mechanisms making a proton transfer reaction more probable along the Pr $\rightarrow$ Pfr reaction than in the parent cationic Pr state. It is found that charge distribution in the cationic species, intra-molecular hydrogen bonding in the neutral, and hydrogen bonding with two highly conserved aspartate and histidine residues have a significant effect on the acidity, while overall chromophore geometry and electronic state are less important factors. Furthermore, based on the calculations, two processes that may facilitate a proton transfer by substantially lowering the pKas relative to their Pr values are identified: (i) a thermal Z,anti $\rightarrow$ Z,syn isomerization at C5, occurring after formation of Lumi-R; (ii) a perturbation of the hydrogen bonding network which in Pr comprises the nitrogens of pyrroles A, B and C and the two aspartate and histidine residues.

• 10.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Nanoscale piezoelectric response of ZnO nanowires measured using a nanoindentation technique2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 26, p. 11113-11118Article in journal (Refereed)

We report the piezoelectric properties of ZnO nanowires (NWs) obtained by using a nanoindenter with a conductive boron-doped diamond tip. The direct piezoelectric effect was measured by performing nanoindentations under load control, and the generated piezoelectric voltage was characterized as a function of the applied loads in the range 0.2-6 mN. The converse piezoelectric effect was measured by applying a DC voltage to the sample while there was a low applied force to allow the tip being always in physical contact with the NWs. Vertically aligned ZnO NWs were grown on inexpensive, flexible, and disposable paper substrates using a template-free low temperature aqueous chemical growth method. When using the nanoindenter to measure the direct piezoelectric effect, piezopotential values of up to 26 mV were generated. Corresponding measurement of the converse piezoelectric effect gave an effective piezoelectric coefficient d(33)(eff) of similar to 9.2 pm V-1. The ZnO NWs were also characterized using scanning electron microscopy, X-ray diffraction, and high-resolution transmission electron microscopy. The new nanoindentation approach provides a straightforward method to characterize piezoelectric material deposited on flexible and disposable substrates for the next generation of nanodevices.

• 11.
Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
KTH Royal Inst Technol, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. KTH Royal Inst Technol, Sweden. KTH Royal Inst Technol, Sweden. Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
Kinetic Monte Carlo simulations of organic ferroelectrics2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 3, p. 1375-1383Article in journal (Refereed)

Ferroelectrics find broad applications, e.g. in non-volatile memories, but the switching kinetics in real, disordered, materials is still incompletely understood. Here, we develop an electrostatic model to study ferroelectric switching using 3D Monte Carlo simulations. We apply this model to the prototypical small molecular ferroelectric trialkylbenzene-1,3,5-tricarboxamide (BTA) and find good agreement between the Monte Carlo simulations, experiments, and molecular dynamics studies. Since the model lacks any explicit steric effects, we conclude that these are of minor importance. While the material is shown to have a frustrated antiferroelectric ground state, it behaves as a normal ferroelectric under practical conditions due to the large energy barrier for switching that prevents the material from reaching its ground state after poling. We find that field-driven polarization reversal and spontaneous depolarization have orders of magnitude different switching kinetics. For the former, which determines the coercive field and is relevant for data writing, nucleation occurs at the electrodes, whereas for the latter, which governs data retention, nucleation occurs at disorder-induced defects. As a result, by reducing the disorder in the system, the polarization retention time can be increased dramatically while the coercive field remains unchanged.

• 12.
University of Strasbourg.
ISOF CNR. UCL. University of Mons. University of Mons. University of Mons. UCL. UCL. UCL. University of Strasbourg. University of Basel. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology. University of Basel. University of Mons. ISOF CNR. UCL. University of Strasbourg.
Photoinduced work function changes by isomerization of a densely packed azobenzene-based SAM on Au: a joint experimental and theoretical study2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 32, p. 14302-14310Article in journal (Refereed)

Responsive monolayers are key building blocks for future applications in organic and molecular electronics in particular because they hold potential for tuning the physico-chemical properties of interfaces, including their energetics. Here we study a photochromic SAM based on a conjugated azobenzene derivative and its influence on the gold work function (Phi(Au)) when chemisorbed on its surface. In particular we show that the Phi(Au) can be modulated with external stimuli by controlling the azobenzene trans/cis isomerization process. This phenomenon is characterized experimentally by four different techniques, kelvin probe, kelvin probe force microscopy, electroabsorption spectroscopy and ultraviolet photoelectron spectroscopy. The use of different techniques implies exposing the SAM to different measurement conditions and different preparation methods, which, remarkably, do not alter the observed work function change (Phi(trans)-Phi(cis)). Theoretical calculations provided a complementary insight crucial to attain a deeper knowledge on the origin of the work function photo-modulation.

• 13.
Royal Inst Technol, SE-10044 Stockholm, Sweden Ctr Chem, Dept Theoret Chem, SE-22100 Lund, Sweden Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
Royal Inst Technol, SE-10044 Stockholm, Sweden Ctr Chem, Dept Theoret Chem, SE-22100 Lund, Sweden Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Royal Inst Technol, SE-10044 Stockholm, Sweden Ctr Chem, Dept Theoret Chem, SE-22100 Lund, Sweden Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
Ab initio modeling of excited state absorption of polyenes2001In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 3, no 13, p. 2567-2575Article in journal (Refereed)

Vertical excitation energies and transition dipole moments between excited electronic states have been calculated for the trans-polyenes series C4H6-C12H14 in order to study the formation of excited state absorption spectra of these species. Quadratic response theory is applied in conjunction with the self-consistent field method and a hierarchical set of coupled-cluster methods. The convergence of the excited state absorption, with respect to wavefunction and treatment of electron correlation and also the length of the oligomer unit, is studied, revealing a considerable demand on the computational effort in order to predict the excited state spectra with precision. The organization of the excited states is found to change in character along the polyene series. The inflexion point for the vertical excitation energies between the one-photon allowed 1(1)B(u) and the two-photon 2(1)A(g) state is predicted to occur between hexatriene and octatetraene. Good agreement with experiment is obtained for butadiene and hexatriene for which the most accurate calculations have been carried out.

• 14.
Royal Inst Technol, SE-10044 Stockholm, Sweden Univ Lund, Ctr Chem, Dept Theoret Chem, SE-22100 Lund, Sweden Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
Royal Inst Technol, SE-10044 Stockholm, Sweden Univ Lund, Ctr Chem, Dept Theoret Chem, SE-22100 Lund, Sweden Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Royal Inst Technol, SE-10044 Stockholm, Sweden Univ Lund, Ctr Chem, Dept Theoret Chem, SE-22100 Lund, Sweden Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
Theoretical calculations of excited state absorption2000In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 2, no 23, p. 5357-5363Article in journal (Refereed)

Excitation energies and transition dipole moments between excited electronic states have been calculated using various theoretical methods to investigate the ability to describe excited state absorption. Quadratic response theory is used in combination with self-consistent field, multi-configurational self-consistent field, and coupled-cluster electronic structure methods. The results of these different methods are compared. The set of molecules considered includes lithium hydride, carbon monoxide, formaldehyde, formamide, and sym-tetrazine. For some of the molecules results are also compared with the method of applying linear response theory to an excited state wavefunction separately optimized by means of the multi-configurational self-consistent field method.

• 15.
University of Trieste, Italy; University of Warsaw, Poland.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering. IPCF CNR, Italy. UPS, France; UPS, France. University of Trieste, Italy; Aarhus University, Denmark.
A complex-polarization-propagator protocol for magneto-chiral axial dichroism and birefringence dispersion2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 19, p. 13267-13279Article in journal (Refereed)

A computational protocol for magneto-chiral dichroism and magneto-chiral birefringence dispersion is presented within the framework of damped response theory, also known as complex polarization propagator theory, at the level of time-dependent Hartree-Fock and time-dependent density functional theory. Magneto-chiral dichroism and magneto-chiral birefringence spectra in the (resonant) frequency region below the first ionization threshold of R-methyloxirane and L-alanine are presented and compared with the corresponding results obtained for both the electronic circular dichroism and the magnetic circular dichroism. The additional information content yielded by the magneto-chiral phenomena, as well as their potential experimental detectability for the selected species, is discussed.

• 16.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
Order and disorder in quaternary atomic laminates from first-principles calculations2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 47, p. 31810-31821Article in journal (Refereed)

We report on the phase stability of chemically ordered and disordered quaternary MAX phases - TiMAlC, TiM2AlC2, MTi2AlC2, and Ti2M2AlC3 where M = Zr, Hf (group IV), M = V, Nb, Ta (group V), and M = Cr, Mo, W (group VI). At 0 K, layered chemically ordered structures are predicted to be stable for M from groups V and VI. By taking into account the configurational entropy, an order-disorder temperature T-disorder can be estimated. TiM2AlC2 (M = Cr, Mo, W) and Ti2M2AlC3 (M = Mo, W) are found with Tdisorder 4 1773 K and are hence predicted to be ordered at the typical bulk synthesis temperature of 1773 K. Other ordered phases, even though metastable at elevated temperatures, may be synthesized by non-equilibrium methods such as thin film growth. Furthermore, phases predicted not to be stable in any form at 0 K can be stabilized at higher temperatures in a disordered form, being the case for group IV, for MTi2AlC2 (M = V, Cr, Mo), and for Ti2M2AlC3 (M = V, Ta). The stability of the layered ordered structures with M from group VI can primarily be explained by Ti breaking the energetically unfavorable stacking of M and C where M is surrounded by C in a face-centered cubic configuration, and by M having a larger electro-negativity than Al resulting in a fewer electrons available for populating antibonding Al-Al orbitals. The results show that these chemically ordered quaternary MAX phases allow for new elemental combinations in MAX phases, which can be used to add new properties to this family of atomic laminates and in turn prospects for tuning these properties.

• 17. Danilczuk, M
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Chemical Physics .
Interaction of silver atoms with ethylene in Ag-SAPO-11 molecular sieve: an EPR and DFT study2004In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 6, no 6, p. 1165-1168Article in journal (Refereed)

The formation of silver-ethylene complexes in dehydrated Ag-SAPO-11 molecular sieve have been observed by electron paramagnetic resonance spectroscopy (EPR) after gamma-irradiation at 77 K. Such reactive intermediate can play an important role in catalytic conversion of ethylene on silver loaded molecular sieves. The Ag(C2H4)(2) stabilized inside relatively small channels of SAPO-11 molecular sieve it is observed even at 290 K. The 'gas-phase' geometries of Ag(C2H4) and Ag(C2H4)(2) complexes, and respective hyperfine coupling constants were calculated applying DFT quantum chemical methods. The hyperfine coupling constants calculated for Ag(C2H4)(2) complex of D-2h symmetry are in very good agreement with those obtained experimentally.

• 18.
Univ Brasilia, Brazil.
Univ Brasilia, Brazil. Univ Brasilia, Brazil. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil. Univ Brasilia, Brazil.
Dynamical exciton decay in organic materials: the role of bimolecular recombination2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 4, p. 1711-1716Article in journal (Refereed)

Excitons play a critical role in light emission when it comes to organic semiconductors. In high exciton concentration regimes, monomolecular and bimolecular routes for exciton recombination can yield different products affecting significantly the materials optical properties. Here, the dynamical decay of excitons is theoretically investigated using a kinetic Monte Carlo approach that addresses singlet exciton diffusion. Our numerical protocol includes two distinct exciton-exciton interaction channels: exciton annihilation and biexciton cascade emission. Our findings reveal that these channels produce different consequences concerning diffusion and spectroscopic properties, being able to explain diverging experimental observations. Importantly, we estimate critical exciton densities for which bimolecular recombination becomes dominant and investigate its effect on average exciton lifetimes and diffusion lengths.

• 19.
University of Siena, Italy and Uppsala University, Sweden.
On the primary event of phytochrome: quantum chemical comparison of photoreactions at C4, C10 and C152009In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, no 9, p. 1354-1361Article in journal (Refereed)

Phytochromes are widespread photoreceptors responsive to red and far-red light that exist in two photochromic forms Pr (inactive) and Pfr (active). The Pr $\rightarrow$ Pfr conversion proceeds through a series of events initiated by Z $\rightarrow$ E photoisomerization of the tetrapyrrole chromophore, believed to occur at C15 of the methine bridge between rings C and D. Recent crystal structures show that ring D in Pr is less tightly packed by the protein than rings A, B and C, which should favor the C15 reaction over reactions at C4 (AB methine bridge) and C10 (BC). In the present work, quantum chemical methods are used to establish the intrinsic reactivity of the chromophore towards all three possible Z $\rightarrow$ E isomerization events in the absence of steric effects and specific interactions with the protein. Using a level of theory that reproduces spectroscopic data with anaccuracy of $\sim$0.2 eV, it is demonstrated that isolated conditions allow the C10 photoreaction to substantially dominate. This finding suggests that the different degrees of ring-packing observed inthe protein are crucial not only to facilitate a reaction at C15, but also to prevent an intrinsically more favorable reaction at C10 from taking place.

• 20.
Uppsala University, Sweden.
Uppsala University, Sweden . Uppsala University, Sweden and Örebro University, Sweden.
Phytochromobilin C15-Z,syn → C15-E,anti isomerization: concerted or stepwise?2004In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 6, no 21, p. 5066-5073Article in journal (Refereed)

The C15-Z,syn $\rightarrow$ C15-E,anti isomerization of phytochromobilin that underlies the photoactivation of phytochrome, the plant photoreceptor responsive to red and far-red light, is investigated by means of quantum chemical methods. By calculating ground and excited-state potential energy surfaces for a phytochromobilin model comprising the full tetrapyrrolic skeleton, and taking into consideration rotations around the C14–C15 and C15=C16 bonds constituting the methine bridge between pyrrole rings C and D, it is found that a stepwise Z $\rightarrow$ E, syn $\rightarrow$ anti mechanism is energetically preferable over a concerted Z,syn $\rightarrow$ E,anti mechanism. In particular, on the basis of the calculated potential energy surfaces, it is proposed that the primary photochemical reaction involves a Z $\rightarrow$ E isomerization only, and that the subsequent syn $\rightarrow$ anti isomerization proceeds thermally.

• 21.
Uppsala University, Sweden.
Uppsala University, Sweden and Örebro University, Sweden .
Conformational dependence of the electronic absorption by astaxanthin and its implications for the bathochromic shift in crustacyanin2004In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 6, no 16, p. 4190-4198Article in journal (Refereed)

The conformational dependence of the electronic absorption by astaxanthin is believed to be of relevance for the bathochromic shift that this carotenoid assumes upon binding to crustacyanin, the protein macromolecular complex responsible for the slate-blue colouration of lobster shell. Here, we report quantum chemical calculations suggesting that the bathochromic shift that can be attributed to changes in astaxanthin conformation brought about by binding to the protein in fact is rather small. In particular, by subjecting an exhaustive set of different astaxanthin conformations to time-dependent density functional theory (TD-DFT) and semiempirical configuration interaction singles (ZINDO/S) calculations, it is found that the bathochromic shift due to the protein-enforced coplanarity of the β-ionone rings with the polyene chain is considerably smaller (TD-DFT: 22–37 nm; ZINDO/S: 11–19 nm) than the >100 nm shift that recently [B. Durbeej and L. A. Eriksson, Chem. Phys. Lett., 2003, 375, 30] was predicted to arise from a hydrogen-bond mediated interaction involving one of the astaxanthin C4 keto groups and a histidine residue of the surrounding protein. Moreover, the calculations suggest that the protein-induced bowing of astaxanthin about the center of the polyene chain is of no relevance for the observed bathochromic shift.

• 22.
University of Siena, Italy.
Örebro University, Sweden.
Protein-bound chromophores astaxanthin and phytochromobilin: excited state quantum chemical studies2006In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 8, no 35, p. 4053-4071Article in journal (Refereed)

We present an overview of excited state quantum chemical calculations aimed at elucidating controversial issues regarding the photochemistry of the protein-bound chromophores astaxanthin and phytochromobilin. In particular, we show how the application of time-dependent density functional theory and other single-reference quantum chemical excited state methods have contributed to shed new light on the origin of the >0.5 eV bathochromic shift of the electronic absorption by the carotenoid astaxanthin in the protein macromolecular complex crustacyanin, and the mechanism for C15-Z,syn $\rightarrow$ C15-E,anti isomerization of the tetrapyrrole phytochromobilin that underlies the photoactivation of the plant photoreceptor phytochrome. Within the approximation that exciton coupling is neglected, the calculations on astaxanthin provide support for the notion that the bathochromic shift, which is responsible for the slate-blue coloration of lobster shell, is due to polarization rather than a conformational change of the chromophore in the protein-bound state. Furthermore, the polarization is attributed to a hydrogen-bonded protonated histidine residue. The calculations on phytochromobilin, in turn, suggest that a stepwise C15-Z,syn $\rightarrow$ C15-E,syn (photochemical), C15-E,syn $\rightarrow$ C15-E,anti (thermal) mechanism is much more favorable than a concerted, fully photochemical mechanism, and that neutral forms of the chromophore are much less likely to photoisomerize than the parent, protonated form. Accordingly, the calculations indirectly support the view that the photoactivation of phytochrome does not involve a proton transfer from the chromophore to the surrounding protein.

• 23. Eid, O.I.
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Chemical Physics . Department of Physics, University of Oslo, PO Box 1048, Blindern, N-0316, Oslo, Norway.
Allyl type radical formation in X-irradiated glutarimide crystals studied by ENDOR and ENDOR-induced EPR2004In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 6, no 13, p. 3604-3610Article in journal (Refereed)

• 24.
University of Copenhagen, Denmark .
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology. Aarhus University, Denmark . University of Copenhagen, Denmark .
Computational study of the Rayleigh light scattering properties of atmospheric pre-nucleation clusters2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 22, p. 10883-10890Article in journal (Refereed)

The Rayleigh and hyper Rayleigh scattering properties of the binary (H2SO4)(H2O)(n) and ternary (H2SO4)(NH3)(H2O) n clusters are investigated using a quantum mechanical response theory approach. The molecular Rayleigh scattering intensities are expressed using the dipole polarizability alpha and hyperpolarizability beta tensors. Using density functional theory, we elucidate the effect of cluster morphology on the scattering properties using a combinatorial sampling approach. We find that the Rayleigh scattering intensity depends quadratically on the number of water molecules in the cluster and that a single ammonia molecule is able to induce a high anisotropy, which further increases the scattering intensity. The hyper Rayleigh scattering activities are found to be extremely low. This study presents the first attempt to map the scattering of atmospheric molecular clusters using a bottom-up approach.

• 25.
University of Copenhagen, Denmark.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering. University of Copenhagen, Denmark.
Rayleigh light scattering properties of atmospheric molecular clusters consisting of sulfuric acid and bases2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 24, p. 15701-15709Article in journal (Refereed)

The Rayleigh light scattering properties of (H2SO4)(a)(NH3)(b) and (H2SO4)(a)((CH3)(2)NH)(b) atmospheric molecular clusters have been investigated using a response theory approach. Using density functional theory the molecular structures and stepwise formation free energies of clusters with a and b up to 4 have been re-investigated. The Rayleigh scattering intensities are calculated from the dipole polarizability tensor a using the CAM-B3LYP functional by applying linear response methods. The intrinsic scattering properties of (H2SO4)(a)(NH3)(b) and (H2SO4)(a)((CH3)(2)NH)(b) indicate that amine containing clusters scatter light significantly more efficiently then their ammonia containing counterparts. Using the Atmospheric Cluster Dynamics Code (ACDC) the steady state cluster concentrations are estimated and the effective scattering is calculated. The effective scattering is shown to be highly dependent on the estimated concentrations and indicates that there exist competitive pathways, such as nucleation and coagulation, which influence the cluster distributions. The frequency dependence of the scattering is found to depend on the cluster composition and show increased responses when clusters contain more bases than acid molecules. Based on structures obtained using semi-empirical molecular dynamics simulations the Rayleigh scattering properties of clusters with up to 20 acid-base pairs are evaluated. This study represents the first step towards gaining a fundamental understanding of the scattering properties of small atmospheric clusters in the ambient atmosphere.

• 26.
Karpov Inst. of Physical Chemistry, Vorontsovo Pole Str. 10, Moscow 103064, Russian Federation, Inst. of Synth. Polymeric Materials, Russian Academy of Sciences, Profsoyuznaya Str. 70, Moscow 117393, Russian Federation.
Karpov Inst. of Physical Chemistry, Vorontsovo Pole Str. 10, Moscow 103064, Russian Federation. Inst. of Synth. Polymeric Materials, Russian Academy of Sciences, Profsoyuznaya Str. 70, Moscow 117393, Russian Federation. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Chemical Physics .
Effect of matrix and substituent on the electronic structure of trapped benzene radical cations2000In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 2, no 1, p. 29-35Article in journal (Refereed)

The structure and dynamics of the radical cations produced from benzene, monodeuterated benzene and toluene in various low-temperature matrices were characterized by EPR and ENDOR spectroscopy. It was found that the nature of the matrix had a dramatic effect on the EPR spectra of benzene cation. Rigid structures corresponding to the 2B(1g) and 2B(2g) states are revealed in solid argon and halocarbon (CFCl3) matrices, respectively, whereas only dynamically averaged patterns are observed in other hosts used (krypton, xenon, sulfur hexafluoride). Deuterium monosubstitution has no appreciable effect on the cation structure observed in argon and halocarbon matrices, which implies matrix control of the preferred electronic state. In contrast, the toluene radical cation exhibits only a 2B(2g)-like structure both in argon and in CFCl3 matrices, that is, the internal structural effect strongly predominates over environment effects in this case. The results are discussed in qualitative terms taking into consideration the matrix and substituent effects on the charge distribution in benzene cation.

• 27.
University of Brasilia, Brazil .
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology. University of Brasilia, Brazil . University of Brasilia, Brazil .
Critical temperature and products of intrachain polaron recombination in conjugated polymers2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 32, p. 17072-17080Article in journal (Refereed)

The intrachain recombination dynamics between oppositely charged polarons is theoretically investigated through the use of a version of the Su-Schrieffer-Heeger (SSH) model modified to include an external electric field, an extended Hubbard model, Coulomb interactions, and temperature effects in the framework of a nonadiabatic evolution method. Our results indicate notable characteristics concerning the polaron recombination: (1) it is found that there exists a critical temperature regime, below which an exciton is formed directly and (2) a pristine lattice is the resulting product of the recombination process, if the temperature is higher than the critical value. Additionally, it is found that the critical electric field regime plays the role of drastically modifying the system dynamics. These facts suggest that thermal effects in the intrachain recombination of polarons are crucial for the understanding of electroluminescence in optoelectronic devices, such as Polymer Light Emitting Diodes.

• 28.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
K- and L-edge X-ray absorption spectrum calculations of closed-shell carbon, silicon, germanium, and sulfur compounds using damped four-component density functional response theory2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 19, p. 13591-13603Article in journal (Other academic)

X-ray absorption spectra of carbon, silicon, germanium, and sulfur compounds have been investigated by means of damped four-component density functional response theory. It is demonstrated that a reliable description of relativistic effects is obtained at both K- and L-edges. Notably, an excellent agreement with experimental results is obtained for L2,3-spectra—with spin-orbit effects well accounted for—also in cases when the experimental intensity ratio deviate from the statistical one of 1:2. The theoretical results are consistent with calculations using standard response theory as well as recently reported real-time propagation methods in time-dependent density functional theory, and the virtues of different approaches are discussed. As compared to silane and silicon tetrachloride, an anomalous error in the absolute energy is reported for the L2,3-spectrum of silicon tetrafluoride, amounting to an additional spectral shift of ~ 1 eV. This anomaly is observed also for other exchange-correlation functionals, but it is seen neither at other silicon edges nor at the carbon K-edge of fluorine derivatives of ethene. Considering the series of molecules SiH4−XFX with X = 1, 2, 3, 4, a gradual divergence from interpolated experimental ionization potentials is observed at the level of Kohn–Sham density functional theory (DFT), and to a smaller extent with use of Hartree–Fock. This anomalous error is thus attributed partly to difficulties in correctly emulating the electronic structure effects imposed by the very electronegative fluorines, and partly due to inconsistencies in the spurious electron self-repulsion in DFT. Substitution with one, or possibly two, fluorine atoms is estimated to yield small enough errors to allow for reliable interpretations and predictions of L2,3-spectra of more complex and extended silicon-based systems.

• 29.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
Fysikum, Stockholm University, Albanova, Stockholm, Sweden. Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste, Trieste, Italy / Aarhus Institute of Advanced Studies, Aarhus University, Aarhus, Denmark. Fysikum, Stockholm University, Albanova, Stockholm, Sweden / Science Institute, University of Iceland, VR-III, Reykjavik, Iceland. Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Fysikum, Stockholm University, Albanova, Stockholm, Sweden.
Requirements of first-principles calculations of X-ray absorption spectra of liquid water2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 1, p. 566-583Article in journal (Refereed)

A computational benchmark study on X-ray absorption spectra of water has been performed by means of transition-potential density functional theory (TP-DFT), damped time-dependent density functional theory (TDDFT), and damped coupled cluster (CC) linear response theory. For liquid water, using TDDFT with a tailored CAM-B3LYP functional and a polarizable embedding, we find that an embedding with over 2000 water molecules is required to fully converge spectral features for individual molecules, but a substantially smaller embedding can be used within averaging schemes. TP-DFT and TDDFT calculations on 100 MD structures demonstrate that TDDFT produces a spectrum with spectral features in good agreement with experiment, while it is more difficult to fully resolve the spectral features in the TP-DFT spectrum. Similar trends were also observed for calculations of bulk ice. In order to further establish the performance of these methods, small water clusters have been considered also at the CC2 and CCSD levels of theory. Issues regarding the basis set requirements for spectrum simulations of liquid water and the determination of gas-phase ionization potentials are also discussed.

• 30.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
Charge generation in polymer-fullerene bulk-heterojunction solar cells2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 38, p. 20291-20304Article in journal (Refereed)

Charge generation in organic solar cells is a fundamental yet heavily debated issue. This article gives a balanced review of different mechanisms proposed to explain efficient charge generation in polymer-fullerene bulk-heterojunction solar cells. We discuss the effect of charge-transfer states, excess energy, external electric field, temperature, disorder of the materials, and delocalisation of the charge carriers on charge generation. Although a general consensus has not been reached yet, recent findings, based on both steady-state and transient measurements, have significantly advanced our understanding of this process.

• 31.
Eindhoven University of Technology, Netherlands.
Katholieke University of Leuven, Belgium. Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. Eindhoven University of Technology, Netherlands. Katholieke University of Leuven, Belgium. Eindhoven University of Technology, Netherlands. Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. Eindhoven University of Technology, Netherlands.
True ferroelectric switching in thin films of trialkylbenzene-1,3,5-tricarboxamide (BTA)2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 34, p. 23663-23672Article in journal (Refereed)

We have investigated the ferroelectric polarization switching properties of trialkylbenzene-1,3,5-tricarboxamide (BTA), which is a model system for a large class of novel organic ferroelectric materials. In the solid state BTAs form a liquid crystalline columnar hexagonal phase that provides long range order that was previously shown to give rise to hysteretic dipolar switching. In this work the nature of the polar switching process is investigated by a combination of dielectric relaxation spectroscopy, depth-resolved pyroelectric response measurements, and classical frequency- and time-dependent electrical switching. We show that BTAs, when brought in a homeotropically aligned hexagonal liquid crystalline phase, are truly ferroelectric. Analysis of the transient switching behavior suggests that the ferroelectric switching is limited by a highly dispersive nucleation process, giving rise to a wide distribution of switching times.

• 32.
Eindhoven University of Technology, the Netherlands.
Eindhoven University of Technology, the Netherlands. Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. KU Leuven, Heverlee, Belgium. KU Leuven, Heverlee, Belgium. Eindhoven University of Technology, the Netherlands. Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering. Eindhoven University of Technology, the Netherlands.
Polarization loss in the organic ferroelectrictrialkylbenzene-1,3,5-tricarboxamide (BTA)2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 4, p. 3192-3200Article in journal (Refereed)

We investigate the polarization loss in the archetypical molecular organic ferroelectric trialkylbenzene-1,3,5-tricarboxamide (BTA). We prove that the polarization loss is due to thermally activated R-relaxation,which is a collective reversal of the amide dipole moments in ferroelectric domains. By applying a weakelectrostatic field both the polarization loss and the R-relaxation are suppressed, leading to anenhancement of the retention time by at least several orders of magnitude. Alternative loss mechanismsare discussed and ruled out. By operating the thin-film devices slightly above the crystalline to liquidcrystalline phase transition temperature the retention time of one compound becomes more than12 hours even in absence of supportive bias, which is among the longest reported so far for organicferroelectric materials.

• 33.
Uppsala University.
Stockholm University. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. Uppsala University. Uppsala University. Royal Institute of Technology. Royal Institute of Technology. Royal Institute of Technology. Uppsala University.
Mapping the frontier electronic structures of triphenylamine basedorganic dyes at TiO2 interfaces2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 8, p. 3534-3546Article in journal (Refereed)

The frontier electronic structures of a series of organic dye molecules containing a triphenylaminemoiety, a thiophene moiety and a cyanoacrylic acid moiety have been investigated byphotoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), X-ray emissionspectroscopy (XES) and resonant photoelectron spectroscopy (RPES). The experimental resultswere compared to electronic structure calculations on the molecules, which are used to confirmand enrich the assignment of the spectra. The approach allows us to experimentally measure andinterpret the basic valence energy level structure in the dye, including the highest occupied energylevel and how it depends on the interaction between the different units. Based on N 1s X-rayabsorption and emission spectra we also obtain insight into the structure of the excited states,the molecular orbital composition and dynamics. Together the results provide an experimentallydetermined energy level map useful in the design of these types of materials. Included are alsoresults indicating femtosecond charge redistribution at the dye/TiO2 interface.

• 34.
Aalto University, Finland.
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology. Surface Science Research Centre, University of Liverpool, UK.
Computational study of the adsorption and dissociation of phenol on Pt and Rh surfaces2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 16, p. 5849-5854Article in journal (Refereed)

The adsorption of phenol on flat and stepped Pt and Rh surfaces and the dissociation of hydrogen from the hydroxyl group of phenol on Pt(111) and Rh(111) were studied by density functional calculations. On both Pt(111) and Rh(111), phenol adsorbs with the aromatic ring parallel to the surface and the hydroxyl group tilted away from the surface. Furthermore, adsorption on stepped surfaces was concluded to be unfavourable compared to the (111) surfaces due to the repulsion of the hydroxyl group from the step edges. Transition state calculations revealed that the reaction barriers, associated with the dissociation of phenol into phenoxy, are almost identical on Pt and Rh. Furthermore, the oxygen in the dissociated phenol is strongly attracted by Rh(111), while it is repelled by Pt(111).

• 35.
Department of Physics, University of Oslo, P.O. Box 1048, Blindern, N-0316, Oslo, Norway.
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Chemical Physics . Department of Physics, University of Oslo, P.O. Box 1048, Blindern, N-0316, Oslo, Norway.
EPR and ENDOR studies of single crystals of 2-oxazolidinone X-irradiated at 295 K2002In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 4, no 24, p. 6086-6091Article in journal (Refereed)

When single crystals of the 5-membered heterocyclic ring structure 2-oxazolidinone (C3O2NH5) are irradiated at room temperature, the major radical formed (R1) decays during a period of a few hours, leaving a broad, unstructured EPR spectrum not amenable to analysis. Cooling the crystals to about 140 K immediately after irradiation at room temperature allows analysis of the R1 radical by EPR and ENDOR. The radical is formed by a net H-abstraction from one of the two methylene groups of the molecule. A full EPR and ENDOR analysis of four proton interactions (one a-coupling, and three ß-couplings) together with ESR evidence for a small nitrogen hyperfine interaction allowed for a precise identification of R1. The results show that the carbon-centered radical R1 is puckered at the radical center. Using DFT calculations together with the experimental EPR and ENDOR results, the torsion angle of the C1-H bond with respect to the N-C1-C2 plane is estimated to be 13-15° (bending angle 0˜ 7°). The DFT calculations reproduced the carbon-bonded proton hyperfine coupling constants satisfactorily but failed to reproduce the experimental results for the nitrogen and nitrogen-bonded proton hyperfine interactions. © The Owner Societies 2002.

• 36. Itagaki, Y.
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Chemical Physics .
Structure of dimeric radical cations of benzene and toluene in halocarbon matrices: An EPR, ENDOR and MO study2000In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 2, no 12, p. 2683-2689Article in journal (Refereed)

The structure of dimeric cations of benzene and toluene formed in X- irradiated halocarbon matrices containing relatively high concentration of the solutes was investigated. EPR and ENDOR (electron nuclear double resonance) spectra of these dimer cations were observed and accurate values of the hf coupling constants were obtained. The ENDOR spectrum of the dimeric radical cation of benzene, (C6H6)2+, exhibited hf couplings due to twelve equivalent protons and the isotropic coupling (a(iso)) was almost one-half of that in the monomer cation. ENDOR transitions with a rhombic symmetry were observed in a CFCl3 matrix, whereas clear axially symmetric transitions with A(is parallel with) < A(is perpendicular to) were obtained in CF3CCl3 even at 50 K. The rhombic dipolar coupling tensor was used as a parameter to evaluate the distance between the two partner rings. As regards the toluene dimer cation, (CH3C6H5)2+, ENDOR transitions of the CH3 and H(4,4') protons were observed. The isotropic hf coupling of the CH3 protons deviated even more strongly from the half value, being rather close to one- third of the value of the monomer. The hf coupling of the H(4,4') protons was almost half the coupling of the monomer. It was suggested that the anomalous hf couplings of the CH3 protons were due to the interaction between the two rings through the s-bond. Density functional theory (DFT) calculations were employed to obtain the optimized geometries and hf coupling tensors and suggested sandwich structures in both dimers. Furthermore, the distances between the two rings and the anomalous CH3 protons hf coupling in the (CH3C6H5)2+ were successfully evaluated.

• 37. Itagaki, Y.
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Chemical Physics . Department of Physics, University of Oslo, N-0316 Oslo, Norway. Institute of Molecular Physics, Polish Academy of Sciences, PL 60-179, Poznan, Poland.
Structure of N2H4.+ formed in X-irradiated Li(N2H5)SO4 single crystals2000In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 2, no 1, p. 37-42Article in journal (Refereed)

X-irradiated Li(N2H5)SO4 single crystals were investigated using ESR and ENDOR spectroscopy at several temperatures. The hydrazine radical cation N2H4.+ was selectively produced by irradiation at room temperature. From the analysis of the orientation dependent ENDOR spectra, the 1H-hfc tensors of the cation radical were precisely obtained and the radical structure was supported by theoretical calculations. It is suggested that the cation radical has a planar p* structure D(2h) (2B(2g)) in the crystal down to 230 K. By using the evaluated 1H-hf tensor the powder ESR line shape was successfully simulated. Concomitant with the radical formation, the N-N bond of N2H4.+ is suggested to reorient so as to optimize hydrogen bond interactions. 1H-ENDOR line splitting for the N2H4.+ radical was observed at temperatures below 230 K. Apparently this splitting is due to a reversible structural change where one of the NH2 moleties in N2H4.+ becomes slightly bent out of the molecular plane, whereas the other one remains planar. This deformation evidently arises from interactions between the cation radical, adjacent H2N-NH3+ molecules and the SO4-LiO4 framework. Interacting N2H5+···N2H4.+···N2H5+ molecules along the c-axis are proposed to explain the deformation mechanism.

• 38.
Hiroshima Univ, Grad Sch Engn, Dept Appl Chem, Higashihiroshima 7398527, Japan Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden.
Hiroshima Univ, Grad Sch Engn, Dept Appl Chem, Higashihiroshima 7398527, Japan Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden. Hiroshima Univ, Grad Sch Engn, Dept Appl Chem, Higashihiroshima 7398527, Japan Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Chemical Physics .
An EPR and ENDOR study of quartet state nitrogen atoms trapped in irradiated NaN3 powder2001In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 3, no 19, p. 4444-4448Article in journal (Refereed)

The nature of quartet state nitrogen atoms formed in gamma -irradiated NaN3 powder was investigated by EPR, ENDOR and ENDOR-induced EPR (EIE). The ENDOR spectrum observed at 110 K clearly showed two sets of N-14 signal pairs centered at a(N)/2 (half the N-14-hyperfine splitting) and at 3a(N)/2, strongly suggesting the existence of quartet state N-14 atoms (S-4(3/2)). At 160 K, the EPR spectrum exhibited a clear fine structure. accompanied by a hyperfine coupling due to N-14. The zero-field splitting, D, gradually increased with decreasing temperature from 170 to 40 K, and then became nearly constant. The temperature dependence of D was explained in terms of a local lattice vibration coupled with spin states of N-14 atoms. At below 95 K, a new fine structure with larger D was observed. The observed two D-values were attributed to 14N atoms located at two different interstitial sites in the monoclinic NaN3 structure.

• 39.
Indian Institute Technology, India .
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology. Indian Institute Technology, India .
Impurity-band induced transport phenomenon and thermoelectric properties in Yb doped PbTe1-xIx2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 39, p. 16686-16692Article in journal (Refereed)

In the present investigation, we report the effect of ytterbium (Yb) impurity band on charge transport and thermoelectric properties in PbTe1-xIx. The temperature dependent interaction of Yb-states with charge carriers and host energy-bands is found to significantly affect the electrical transport parameters in all the investigated samples. Our result indicates that, in the presence of Yb band, the carrier concentration did not increase as effectively as it was found in pristine PbTe with increasing iodine content. An anomalous switching of positive thermopower into negative was found in the samples with lower iodine content. Such phenomena were explained by the redistribution of charge carriers within the different available bands and promotion of vacancy like defects via substitutional impurity. Due to the optimum doping levels, the sample with the highest iodine content showed a decent figure of merit with a peak value of 0.69 at 575 K in the sample with x = 0.007.

• 40.
Univ Kaiserslautern, Germany.
Univ Kaiserslautern, Germany. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. Wuhan Inst Technol, Peoples R China. Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering. Univ Kaiserslautern, Germany.
Electronic and magnetic properties of a ferromagnetic cobalt surface by adsorbing ultrathin films of tetracyanoethylene2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 28, p. 15833-15844Article in journal (Refereed)

Ultrathin films of tetracyanoethylene (TCNE) on Co(100) were investigated by means of spin-integrated and spin-resolved photoemission spectroscopy ((sp-)UPS), X-ray photoemission spectroscopy (XPS), near edge X-ray absorption fine-structure spectroscopy (NEXAFS), and X-ray magnetic circular dichroism (XMCD). We found a coverage-dependent modulation of the interface dipole and a switching between a metallic and a resistive spin filtering at the interface triggered by two distinct adsorption geometries of TCNE. The strongest hybridization and spin structure modifications are found at low coverage with a face-on adsorption geometry indicating changes in the distance between the surface Co atoms beneath. TCNE has the potential to manipulate the magnetic moments in the Co surface itself, including the possibility of magnetic hardening effects. In summary, the system TCNE/Co offers an experimentally rather easy and controllable way to build up a stable molecular platform stabilizing the reactive ferromagnetic Co surface and customizing the electronic and magnetic properties of the resulting spinterface simultaneously. This makes this system very attractive for spintronic applications as an alternative, less reactive but highly spin polarized foundation beside graphene-based systems.

• 41.
Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry . Linköping University, The Institute of Technology.
A theoretical study of water clusters: the relation between hydrogen-bond topology and interaction energy from quantum-chemical computations for clusters with up to 22 molecules2005In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 7, p. 1905-1911Article in journal (Refereed)

Quantum-chemical calculations of a variety of water clusters with eight, ten and twelve molecules were performed, as well as for selected clusters with up to 22 water molecules. Geometry optimizations were carried out at the B3LYP/cc-pVDZ level and single-point energies were calculated at the B3LYP/aug-cc-pVDZ level for selected clusters. The electronic energies were studied with respect to the geometry of the oxygen arrangement and six different characteristics of the hydrogen-bond arrangement in the cluster. Especially the effect of the placement of the non-hydrogen bonding hydrogens on the interaction energy was studied. Models for the interaction energy with respect to different characteristics of the hydrogen-bond arrangement were derived through least-square fits. The results from the study of the clusters with eight, ten and twelve molecules are used to predict possible low-energy structures for various shapes of clusters with up to 22 molecules.

• 42.
Hiroshima Univ, Grad Sch Engn, Dept Appl Chem, Higashihiroshima 7398527, Japan Inst Nucl Chem & Technol, Dept Radiat Chem & Technol, PL-03195 Warsaw, Poland Linkoping Univ, Dept Phys & Measurement Technol, Chem Phys Lab, S-58183 Linkoping, Sweden.
Hiroshima Univ, Grad Sch Engn, Dept Appl Chem, Higashihiroshima 7398527, Japan Inst Nucl Chem & Technol, Dept Radiat Chem & Technol, PL-03195 Warsaw, Poland Linkoping Univ, Dept Phys & Measurement Technol, Chem Phys Lab, S-58183 Linkoping, Sweden. Hiroshima Univ, Grad Sch Engn, Dept Appl Chem, Higashihiroshima 7398527, Japan Inst Nucl Chem & Technol, Dept Radiat Chem & Technol, PL-03195 Warsaw, Poland Linkoping Univ, Dept Phys & Measurement Technol, Chem Phys Lab, S-58183 Linkoping, Sweden. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Chemical Physics .
Cage effect on stability and molecular dynamics of [(CH3)(3)N](center dot+) and [(CH3)(3)NCH2](center dot+) generated in gamma-irradiated zeolites2001In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 3, no 17, p. 3532-3535Article in journal (Refereed)

An EPR study was carried out to elucidate the zeolite cage effect on the stability and molecular dynamics of [(CH3)(3)N](.+) and [(CH3)(3)NCH2](.+) radical cations generated in gamma -irradiated Al-offretite, SAPO-37 and SAPO-42, which contained (CH3)(4)N+ ions as organic template. The [(CH3)(3)N](.+) radical cation was stable at room temperature when it was generated in relatively small size cages such as the sodalite cages of SAPO-37 and the beta -cages of SAPO-42. On the other hand, the [(CH3)(3)NCH2](.+) radical cation was stable not only in the sodalite cages of SAPO-37, but also in relatively large cages such as gmelinite cages or the main channels of Al-offretite and the alpha -cages of SAPO-42. Strongly temperature dependent EPR spectra were observed for the [(CH3)(3)NCH2](.+) radical cation stabilized in Al-offretite and SAPO-42. They were successfully analyzed by a spectral simulation method assuming a three-site exchange for the methyl protons. The evaluated exchange rates were in the order SAPO-37 (sodalite cages) < Al-offretite (gmelinite cages or main channels) < SAPO-42 (alpha -cages) in the temperature range 110-300 K.

• 43.
Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan.
Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan. Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan. Department of Applied Chemistry, Faculty of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan. Dept. of Radiat. Chem. and T., Inst. of Nucl. Chem. and Technology, 03-195 Warsaw, Dorodna 16, Poland. Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Chemical Physics .
Structure and dynamics of [(CH3)3N-CH2]+· radical generated in ?- irradiated Al-offretite2000In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 2, no 11, p. 2515-2519Article in journal (Refereed)

An EPR study was carried out to investigate the structure and motional dynamics of the [(CH3)3N-CH2]+· radical formed in a ?-irradiated Al- offretite. Strongly temperature-dependent EPR spectra were observed in the temperature range between 4 and 300 K. The observed 1H hyperfine (hf) splitting was a1 = 0.46 mT for three magnetically equivalent hydrogens, one of each methyl group at 110 K and a1 = 0.15 mT for three of each methyl group at 300 K, the hf splittings due to two equivalent CH2 hydrogens and the central 14N were a2 = 2.24 and a3 = 0.35 mT, respectively, independent of the temperature. This result suggests that rotation of the methyl group around the N-CH3 bond is responsible for the temperature dependent line shapes. Assuming a three-site jump model in which three methyl protons interchange their positions with each other, the EPR line shapes were successfully analyzed by a simulation method using the jump rate as a variable parameter in the temperature range from 140 to 270 K. The rate was found to increase from 7.0 x 106 s-1 (140 K) to 4.1 x 108 s-1 (270 K) with temperature. From an Arrhenius plot of the rate constants, an activation energy of 8.1 kJ mol-1 was evaluated for the methyl group rotation of [(CH3)3N-CH2]+· in Al-offretite.

• 44.
Hiroshima Univ, Grad Sch Engn, Dept Appl Chem, Higashihiroshima 7398527, Japan Inst Nucl Chem & Technol, Dept Radiat Chem & Technol, PL-03195 Warsaw, Poland Linkoping Univ, Dept Phys & Measurement Technol, Chem Phys Lab, S-58183 Linkoping, Sweden.
Structure and dynamics of triethylamine and tripropylamine radical cations generated in AlPO4-5 by ionizing radiation: an EPR and MO study2001In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 3, no 9, p. 1611-1616Article in journal (Refereed)

An EPR study was carried out to investigate both the structure and molecular dynamics of triethylamine (Et3N) and tripropylamine (Pr3N) radical cations generated in gamma -irradiated AlPO4-5 from neutral mother molecules incorporated as an organic template. Both Et3N+. and Pr3N+. radical cations were stable at 300 K and showed strongly temperature-dependent EPR spectral line-shapes in the temperature range from 77 to 300 K. The spectral change was successfully explained by assuming a two-site exchange model in which two inequivalent beta -hydrogens interchange their positions with each other. The experimental spectra were quantitatively analyzed by a simulation method using the exchange rate as a variable parameter. From an Arrhenius plot of the rate constants, activation energies of 9.1 and 11.4 kJ mol(-1) were evaluated for Et3N+. and Pr3N+. in AlPO4-5, respectively.

• 45.
Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering. Beijing Univ Chem Technol, Peoples R China.
Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
Clathrate ice sL: a new crystalline phase of ice with ultralow density predicted by first-principles phase diagram computations2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 12, p. 8333-8340Article in journal (Refereed)

In contrast to the rich knowledge of water and 17 experimentally confirmed crystalline phases of solid water under positive pressures, water under negative pressure has been poorly explored. In this study, a new crystalline phase of ice with ultralow density (0.6 g cm(-3)), named clathrate ice sL, is constructed by nano water cage clusters, and it is predicted to be stable under a lower negative pressure than the experimentally confirmed sII phase by first-principles phase diagram computations, thereby extending the phase diagram of water to negative pressure regions below -5170 bar at 0 K and below -4761 bar at 300 K. In addition, according to our theoretical prediction, the optimal hydrogen storage mass density in the new clathrate ice sL is 7.7 wt% (larger than the 2017 DOE target of 5.5 wt%), which would set a new record of hydrogen storage capacity in clathrate hydrates. The finding of clathrate ice sL not only proposes a new type of crystalline ice under negative pressure but also explores the potential applications of the ultralow density ice phases while extending the water phase diagram and enriching the knowledge of people about water.

• 46.
Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, Faculty of Science & Engineering. University of Politecn Cartagena, Spain.
University of Politecn Cartagena, Spain. Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, Faculty of Science & Engineering.
Electrochemo-dynamical characterization of polypyrrole actuators coated on gold electrodes2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 2, p. 827-836Article in journal (Refereed)

Polypyrrole coated gold wires were subjected to consecutive square current waves in LiClO4 aqueous solutions using the same constant anodic and cathodic charge. Parallel in situ diameter variations were followed using a laser scan micrometer. The procedure was repeated by changing one experimental variable every time: applied current, electrolyte concentration or working temperature to perform electrochemodynamical characterization of the system. On average, the diameter follows a linear variation of the consumed charge, as expected for any faradaic system, although a high dispersion was attained in the data. Such deviations were attributed to the presence of irreversible hydrogen evolution at the gold/polypyrrole interface at cathodic potentials more than 0.0 V vs. Ag/AgCl, detected and quantified from separated coulovoltammetric responses. Despite this parallel hydrogen evolution the consumed energy during reactions is a robust sensor of the working conditions. In conclusion a gold support, the metal most used for technological applications of conducting polymers, should be avoided when a device is driven by current flow in the presence of aqueous solutions, water contamination or moisture: a fraction of the charge will be consumed by hydrogen generation with possible degradation of the device.

• 47.
University of Coimbra, Portugal .
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology. University of Coimbra, Portugal . University of Coimbra, Portugal .
Marine natural products from the deep Pacific as potential non-linear optical chromophores2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 35, p. 14814-14822Article in journal (Refereed)

Theoretical analysis using quadratic response theory within the time-dependent density functional theory (TDDFT) formalism shows that the dermacozines, a group of phenazine-based compounds isolated from cultures of Dermacoccus abyssi found in the Mariana Trench, possess large first hyperpolarisability (beta) values at common incident laser wavelengths that are highly sensitive to the degree and type of substitution of the core structure. The phenazine moiety is a versatile and tunable chromophore for non-linear optics and this work serves to highlight the potential that (marine) natural products, even those found in the darkest places on the planet, may have for aiding developments in optical materials design.

• 48.
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Autonomous Univ Madrid, Spain. Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
Computational microscopy study of the granular structure and pH dependence of PEDOT:PSS2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 12, p. 6699-6711Article in journal (Refereed)

Computational microscopy based on Martini coarse grained molecular dynamics (MD) simulations of a doped conducting polymer poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (best known as PEDOT:PSS) was performed focussing on the formation of the granular structure and PEDOT crystallites, and the effect of pH on the material morphology. The PEDOT:PSS morphology is shown to be sensitive to the initial distribution of PEDOT and PSS in the solution, and the results of the modelling suggest that the experimentally observed granular structure of PEDOT:PSS can be only obtained if the PEDOT/PSS solution is in the dispersive state in the initial crystallization stages. Variation of the pH is demonstrated to strongly affect the morphology of PEDOT:PSS films, altering their structure between granular-type and homogeneous. It also affects the size of crystallites and the relative arrangement of PEDOT and PSS chains. It is shown that the crystallites in PEDOT:PSS are smaller than those in PEDOT with molecular counterions such as PEDOT:tosylate, which is consistent with the available experimental data. The predicted changes of the PEDOT:PSS morphology with variation of the pH can be tested experimentally, and the calculated atomistic picture of PEDOT:PSS films (not accessible by conventional experimental techniques) is instrumental for understanding the material structure and building realistic models of PEDOT:PSS morphology.

• 49.
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Ferdowsi Univ Mashhad, Iran.
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
Morphology and ion diffusion in PEDOT:Tos. A coarse grained molecular dynamics simulation2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 25, p. 17188-17198Article in journal (Refereed)

A Martini coarse-grained Molecular Dynamics (MD) model for the doped conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is developed. The morphology of PEDOT:Tos (i.e. PEDOT doped with molecular tosylate) and its crystallization in aqueous solution for different oxidation levels were calculated using the developed method and compared with corresponding all atomistic MD simulations. The diffusion coefficients of Na+ and Cl- ions in PEDOT:Tos are studied using the developed coarse-grained MD approach. It is shown that the diffusion coefficients decrease exponentially as the hydration level is reduced. It is also predicted that the diffusion coefficients decrease when the doping level of PEDOT is increased. The observed behavior is related to the evolution of water clusters and trapping of ions around the polymer matrix as the hydration level changes. The predicted behavior of the ionic diffusion coefficients can be tested experimentally, and we believe that molecular picture of ionic diffusion in PEDOT unraveled in the present study is instrumental for the design of polymeric materials and devices for better and enhanced performance.

• 50.
Ankara Univ, Turkey.
Ankara Univ, Turkey. Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Ferdowsi Univ Mashhad, Iran. Ankara Univ, Turkey.
Electronic structure and optical properties of novel monolayer gallium nitride and boron phosphide heterobilayers2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 44, p. 28124-28134Article in journal (Refereed)

Motivated by the increasing number of studies on optoelectronic applications of van der Waals (vdW) heterostructures, we have investigated the electronic and optical properties of monolayer gallium nitride (MGaN) and boron phosphide (MBP) heterobilayers by using first-principle calculations based on density functional theory. We have ensured the dynamical stability of the structures by considering their binding energies and phonon spectra. We show that the magnitude and status (direct or indirect) of the band gap are strongly dependent on the stacking pattern of the heterobilayers. Furthermore, we have investigated the band splittings in the presence of an external electric field which show the effect of the field on the band alignment of the structure. We have also shown the band gap, charge redistributions and work function of the structures are highly dependent on the magnitude and direction of the electric field such that its magnitude yields indirect to direct band gap transitions around |E-perpendicular to| approximate to 0.7 V angstrom(-1) at the point and the order of the band gap is varied according to the direction of the electric field. Moreover, we examine optical properties of MGaN/MBP heterobilayers as part of DFT calculations. The band gap and work function being tunable with changes in the external field together with the prominent absorption over the UV range make the MGaN/MBP heterobilayer a feasible candidate for optoelectronic applications.

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