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Stafström, Sven
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Publications (10 of 124) Show all publications
Volpi, R., Kottravel, S., Norby, M. S., Stafström, S. & Linares, M. (2016). Effect of Polarization on the Mobility of C60: A Kinetic Monte-Carlo Study. Journal of Chemical Theory and Computation, 12(2), 812-824.
Open this publication in new window or tab >>Effect of Polarization on the Mobility of C60: A Kinetic Monte-Carlo Study
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2016 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 12, no 2, 812-824 p.Article in journal (Refereed) Published
Abstract [en]

We present a study of mobility field and temperature dependence for C60 with Kinetic Monte-Carlo simulations. We propose a new scheme to take into account polarization effects in organic materials through atomic induced dipoles on nearby molecules. This leads to an energy correction for the single site energies and to an external reorganization happening after each hopping. The inclusion of polarization allows us to obtain a good agreement with experiments for both mobility field and temperature dependence.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-122989 (URN)10.1021/acs.jctc.5b00975 (DOI)000370112900032 ()
Note

Vid tiden för disputation förelåg publikationen endast som manuskript

Funding agencies:  SeRC (Swedish e-Science Research Center)

Available from: 2015-12-01 Created: 2015-12-01 Last updated: 2017-12-01Bibliographically approved
Ribeiro, L. A. & Stafström, S. (2016). Impact of the electron-phonon coupling symmetry on the polaron stability and mobility in organic molecular semiconductors. Physical Chemistry, Chemical Physics - PCCP, 18(3), 1386-1391.
Open this publication in new window or tab >>Impact of the electron-phonon coupling symmetry on the polaron stability and mobility in organic molecular semiconductors
2016 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 3, 1386-1391 p.Article in journal (Refereed) Published
Abstract [en]

The influence of the interplay between symmetric and antisymmetric inter-molecular electron-phonon (e-ph) coupling mechanisms on the polaron stability and mobility in organic semiconductors has been theoretically investigated at a molecular level. A semi-empirical Holstein-Peierls model is used which in addition to the symmetric and antisymmetric inter-molecular e-ph interactions also includes an antisymmetric intra-molecular e-ph coupling. Our results show that the symmetric e-ph coupling plays the role of destabilizing the polaron as a result of temperature induced phonons that, via the symmetric coupling, affects the charge distribution of the polaron. Considering this kind of coupling, the parameter space for which the polaron is dynamically stable is strongly temperature-dependent. For the combination of symmetric e-ph coupling strength and temperature, which results in a stable polaron, the velocity of the polaron, and therefore also the charge carrier mobility, is not affected by the symmetric e-ph coupling strength.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2016
National Category
Physical Chemistry
Identifiers
urn:nbn:se:liu:diva-125686 (URN)10.1039/c5cp06577a (DOI)000369482100002 ()26674995 (PubMedID)
Note

Funding Agencies|Swedish Research Council (VR); Brazilian Research Council CAPES; Brazilian Research Council FAPDF

Available from: 2016-03-01 Created: 2016-02-29 Last updated: 2017-11-30
Vinicius Da Costa Medeiros, P., Kostov Gueorguiev, G. & Stafström, S. (2015). Bonding, charge rearrangement and interface dipoles of benzene, graphene, and PAH molecules on Au(111) and Cu(111). Carbon, 81, 620-628.
Open this publication in new window or tab >>Bonding, charge rearrangement and interface dipoles of benzene, graphene, and PAH molecules on Au(111) and Cu(111)
2015 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 81, 620-628 p.Article in journal (Refereed) Published
Abstract [en]

We perform a theoretical study of the electronic properties of polyaromatic hydrocarbon (PAH) molecules, as well as benzene and graphene, adsorbed on copper and gold. The PAH molecules studied are coronene (C24H12), circumcoronene (C54H18) and circumcircumcoronene (C96H24), which we consider as gradual approximations to an infinite graphene layer. In order to understand how the size of the adsorbed PAH molecules influences the adsorbate-metal interactions, we generalize the approach used in our earlier study [Phys Rev B, 85 (2012), p. 205423] to decompose the binding energies and net charge transfers into separate contributions from specific groups of atoms, and we then show that the zigzag edges of the PAH molecules interact stronger with the metal surfaces than the armchair ones. We discuss the nature of binding in our model systems as well as the formation of interface dipoles. We show that for all model systems studied here, the charge rearrangement contribution to the interface dipoles can be expressed as the product of the charge involved in the formation of the dipole and the distance between well-defined centers of charge for electron accumulation and depletion. This distance is only marginally dependent on the specific PAH molecules, decreasing slowly with their size.

Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-113164 (URN)10.1016/j.carbon.2014.09.096 (DOI)000345682900066 ()
Note

Funding Agencies|Swedish Research Council (VR); Linkoping Linnaeus Initiative on Novel Functionalized Materials (VR); Swedish Foundation for Strategic Research (SSF) [RMA11-0029]; FunMat (Functional Nanoscale Materials) - a VINN Excellence Centre (Swedish Agency for Innovation Systems VINNOVA)

Available from: 2015-01-14 Created: 2015-01-12 Last updated: 2017-12-05
Antonio Ribeiro, L. & Stafström, S. (2015). Polaron stability in molecular semiconductors: theoretical insight into the impact of the temperature, electric field and the system dimensionality. Physical Chemistry, Chemical Physics - PCCP, 17(14), 8973-8982.
Open this publication in new window or tab >>Polaron stability in molecular semiconductors: theoretical insight into the impact of the temperature, electric field and the system dimensionality
2015 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 14, 8973-8982 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2015
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-117397 (URN)10.1039/c4cp06028h (DOI)000351933600050 ()25746667 (PubMedID)
Funder
Swedish Research Council
Available from: 2015-04-24 Created: 2015-04-24 Last updated: 2017-12-04Bibliographically approved
Volpi, R., Stafström, S. & Linares, M. (2015). Transition fields in organic materials: From percolation to inverted Marcus regime. A consistent Monte Carlo simulation in disordered PPV. Journal of Chemical Physics, 142(9), 094503.
Open this publication in new window or tab >>Transition fields in organic materials: From percolation to inverted Marcus regime. A consistent Monte Carlo simulation in disordered PPV
2015 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 9, 094503- p.Article in journal (Refereed) Published
Abstract [en]

In this article, we analyze the electric field dependence of the hole mobility in disordered poly (p-phenylene vinylene). The charge carrier mobility is obtained from Monte Carlo simulations. Depending on the field strength three regions can be identified: the percolation region, the correlation region, and the inverted region. Each region is characterized by a different conduction mechanism and thus a different functional dependence of the mobility on the electric field. Earlier studies have highlighted that Poole-Frenkel law, which appears in the correlation region, is based on the type of correlation caused by randomly distributed electric dipoles. This behavior is thus observed in a limited range of field strengths, and by studying a broader range of electric fields, a more fundamental understanding of the transport mechanism is obtained. We identify the electric fields determining the transitions between the different conduction mechanisms in the material and we explain their physical origin. In principle, this allows us to characterize the mobility field dependence for any organic material. Additionally, we study the charge carrier trapping mechanisms due to diagonal and off-diagonal disorder, respectively. (C) 2015 AIP Publishing LLC.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-117234 (URN)10.1063/1.4913733 (DOI)000350973900041 ()25747090 (PubMedID)
Note

Funding Agencies|Swedish Research Council (VR); MATTER Network; SERC (Swedish e-Science Research Center)

Available from: 2015-04-22 Created: 2015-04-21 Last updated: 2017-12-04
Ribeiro, L. A., Ferreira da Cunha, W., Luciano de Almeida Fonseca, A., Magela e Silva, G. & Stafström, S. (2015). Transport of Polarons in Graphene Nanoribbons. Journal of Physical Chemistry Letters, 6(3), 510-514.
Open this publication in new window or tab >>Transport of Polarons in Graphene Nanoribbons
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2015 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, no 3, 510-514 p.Article in journal (Refereed) Published
Abstract [en]

The field-induced dynamics of polarons in armchair graphene nanoribbons (GNRs) is theoretically investigated in the framework of a two-dimensional tight-binding model with lattice relaxation. Our findings show that the semiconductor behavior, fundamental to polaron transport to take place, depends upon of a suitable balance between the GNR width and the electronphonon (eph) coupling strength. In a similar way, we found that the parameter space for which the polaron is dynamically stable is limited to an even narrower region of the GNR width and the eph coupling strength. Interestingly, the interplay between the external electric field and the eph coupling plays the role to define a phase transition from subsonic to supersonic velocities for polarons in GNRs.

Place, publisher, year, edition, pages
American Chemical Society, 2015
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-115322 (URN)10.1021/jz502460g (DOI)000349137400035 ()
Note

Funding Agencies|Swedish Research Council (VR); CNPq; CAPES; FINATEC

Available from: 2015-03-13 Created: 2015-03-13 Last updated: 2017-12-04
Medeiros, P. V., Tsirpin, S. S., Stafström, S. & Björk, J. (2015). Unfolding spinor wave functions and expectation values of general operators: Introducing the unfolding-density operator. Physical Review B. Condensed Matter and Materials Physics, 91, 041116(R)-041120(R).
Open this publication in new window or tab >>Unfolding spinor wave functions and expectation values of general operators: Introducing the unfolding-density operator
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, 041116(R)-041120(R) p.Article in journal (Refereed) Published
Abstract [en]

We show that the spectral weights W mK ⃗ (k ⃗ ) used for the unfolding of two-component spinor eigenstates ∣ ∣ ψ SC mK ⃗ ⟩=|α⟩|ψ SC mK ⃗ ,α⟩+|β⟩|ψ SC mK ⃗ ,β⟩ can be decomposed as the sum of the partial spectral weights W μ mK ⃗ (k ⃗ ) calculated for each component μ=α,β independently, effortlessly turning a possibly complicated problem involving two coupled quantities into two independent problems of easy solution. Furthermore, we define the unfolding-density operator ρ ˆ K ⃗ (k ⃗ ;ɛ) , which unfolds the primitive cell expectation values φ pc (k ⃗ ;ɛ) of any arbitrary operator φ ˆ according to φ pc (k ⃗ ;ɛ)=Tr(ρ ˆ K ⃗ (k ⃗ ;ɛ)φ ˆ ) . As a proof of concept, we apply the method to obtain the unfolded band structures, as well as the expectation values of the Pauli spin matrices, for prototypical physical systems described by two-component spinor eigenfunctions.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-114465 (URN)10.1103/PhysRevB.91.041116 (DOI)000348477200002 ()
Note

P. V. C. M, S. S., and J.B. acknowledge the Swedish Research Council (VR) for funding. S. S. T. acknowledges funding from the University of Basque Country UPV/EHU (GIC07-IT-756-13), the Departamento de Educacion del Gobierno Vasco and the Spanish Ministerio de Ciencia e Innovacion (FIS2010-19609-C02-01), the Tomsk State University Competitiveness Improvement Program, the Saint Petersburg State University (project 11.50.202.2015) and the Spanish Ministry of Economy and Competitiveness MINECO (FIS2013-48286-C2-1-P). Computer resources were allocated by the National Supercomputer Centre, Sweden, through SNAC and the MATTER consortium, as well as in the SKIF-Cyberia and CRYSTAL supercomputers at Tomsk State University.

Available from: 2015-02-20 Created: 2015-02-20 Last updated: 2017-12-04
Palma, C.-A., Björk, J., Klappenberger, F., Arras, E., Kühne, D., Stafström, S. & Barth, J. V. (2015). Visualization and thermodynamic encoding of single-molecule partition function projections. Nature Communications, 6(6210).
Open this publication in new window or tab >>Visualization and thermodynamic encoding of single-molecule partition function projections
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2015 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, no 6210Article in journal (Refereed) Published
Abstract [en]

Ensemble averaging of molecular states is fundamental for the experimental determination of thermodynamic quantities. A special case occurs for single-molecule investigations under equilibrium conditions, for which free energy, entropy and enthalpy at finite temperatures are challenging to determine with ensemble averaging alone. Here we report a method to directly record time-averaged equilibrium probability distributions by confining an individual molecule to a nanoscopic pore of a two-dimensional metal-organic nanomesh, using temperature-controlled scanning tunnelling microscopy. We associate these distributions with partition function projections to assess real-space-projected thermodynamic quantities, aided by computational modelling. The presented molecular dynamics-based analysis is able to reproduce experimentally observed projected microstates with high accuracy. By an in silico customized energy landscape, we demonstrate that distinct probability distributions can be encrypted at different temperatures. Such modulation provides means to encode and decode information into position–temperature space.

Place, publisher, year, edition, pages
Nature Publishing Group, 2015
National Category
Physical Chemistry Condensed Matter Physics Theoretical Chemistry
Identifiers
urn:nbn:se:liu:diva-114477 (URN)10.1038/ncomms7210 (DOI)000350201100019 ()25703681 (PubMedID)
Available from: 2015-03-01 Created: 2015-02-23 Last updated: 2017-12-04
Björk, J. & Stafström, S. (2014). Adsorption of large hydrocarbons on coinage metals: a van der Waals density functional study. ChemPhysChem, 15(13), 2851-2858.
Open this publication in new window or tab >>Adsorption of large hydrocarbons on coinage metals: a van der Waals density functional study
2014 (English)In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, no 13, 2851-2858 p.Article in journal (Refereed) Published
Abstract [en]

The adsorption of organic molecules onto the close-packed facets of coinage metals is studied, and how accurately adsorption heights can be described by using recent advances of the van der Waals density functional (vdWDF), with optPBE/vdWDF, optB86b/vdWDF, vdWDF2, and rev/vdWDF2 functionals is illustrated. The adsorption of two prototypical aromatic hydrocarbons is investigated, and the calculated adsorption heights are compared to experimental literature values from normal incident X-ray standing wave absorption and a state-of-the-art semi-empirical method. It is shown that both the optB86b/vdWDF and rev/vdWDF2 functionals describe adsorption heights with an accuracy of 0.1 Å, compared to experimental values, and are concluded as reliable methods of choice for related systems.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2014
Keyword
density functional calculations, metal–organic interfaces, adsorption, van der waals density functional, van der waals interactions
National Category
Condensed Matter Physics Physical Chemistry Theoretical Chemistry
Identifiers
urn:nbn:se:liu:diva-107770 (URN)10.1002/cphc.201402063 (DOI)000341565600029 ()25044659 (PubMedID)
Available from: 2014-06-19 Created: 2014-06-19 Last updated: 2017-12-05
Goyenola, C., Stafström, S., Schmidt, S., Hultman, L. & Gueorguiev, G. K. (2014). Carbon Fluoride, CFx: Structural Diversity as Predicted by First Principles. The Journal of Physical Chemistry C, 118(12), 6514-6521.
Open this publication in new window or tab >>Carbon Fluoride, CFx: Structural Diversity as Predicted by First Principles
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2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 12, 6514-6521 p.Article in journal (Refereed) Published
Abstract [en]

Fluorinated carbon-based thin films offer a wide range of properties for many technological applications that depend on the microstructure of the films. To gain a better understanding of the role of fluorine in the structural formation of these films, CFx systems based on graphene-like fragments were studied by first-principles calculations. Generally, the F concentration determines the type of film that can be obtained. For low F concentrations (up to similar to 5 at. %), films with fullerene-like as well as graphite-like features are expected. Larger F concentrations (greater than= 10 at. %) give rise to increasingly amorphous carbon films. Further increasing the F concentration in the films leads to formation of a polymer-like microstructure. To aid the characterization of CFx systems generated by computational methods, a statistical approach is developed.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106285 (URN)10.1021/jp500653c (DOI)000333578300060 ()
Available from: 2014-05-06 Created: 2014-05-05 Last updated: 2017-12-05Bibliographically approved
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