liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Time-dependent molecular properties in the optical and x-ray regions
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Time-dependent molecular properties are important for the experimental characterization of molecular materials. We show how these properties can be calculated, for optical and x-ray frequencies, using novel quantum chemical methods. For xray absorption there are important relativistic effects appearing, due to the high velocity electrons near the atomic nuclei. These effects are treated rigorously within the four-component static exchange approximation. We also show how electron correlation can be taken into account in the calculation of x-ray absorption spectra, in time-dependent density functional theory based on the complex polarization propagator approach. The methods developed have been applied to systems of experimental interest|molecules in the gas phase and adsorbed on metal surfaces. The effects of molecular vibrations have been take into account both within and beyond the harmonic approximation.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2007.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1131
Keyword [en]
Quantum chemistry, molecular physics, x-ray spectroscopy, relativity
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:liu:diva-10125ISBN: 978-91-85895-88-5 (print)OAI: oai:DiVA.org:liu-10125DiVA: diva2:16872
Public defence
2007-10-23, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2009-04-26
List of papers
1. Core-shell photoabsorption and photoelectron spectra of gas-phase pentacene: Experiment and theory
Open this publication in new window or tab >>Core-shell photoabsorption and photoelectron spectra of gas-phase pentacene: Experiment and theory
Show others...
2005 (English)In: Journal of chemical physics Online, ISSN 1089-7690, Vol. 122, no 12, 124305- p.Article in journal (Refereed) Published
Abstract [en]

The C K-edge photoabsorption and 1s core-level photoemission of pentacene (C22H14) free molecules are experimentally measured, and calculated by self-consistent-field and static-exchange approximation ab initio methods. Six nonequivalent C atoms present in the molecule contribute to the C 1s photoemission spectrum. The complex near-edge structures of the carbon K-edge absorption spectrum present two main groups of discrete transitions between 283 and 288  eV photon energy, due to absorption to * virtual orbitals, and broader structures at higher energy, involving * virtual orbitals. The sharp absorption structures to the * empty orbitals lay well below the thresholds for the C 1s ionizations, caused by strong excitonic and localization effects. We can definitely explain the C K-edge absorption spectrum as due to both final (virtual) and initial (core) orbital effects, mainly involving excitations to the two lowest-unoccupied molecular orbitals of * symmetry, from the six chemically shifted C 1s core orbitals. ©2005 American Institute of Physics

Keyword
organic compounds, photoexcitation, photoelectron spectra, SCF calculations, ab initio calculations, chemical shift, molecular electronic states, molecule-photon collisions
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12685 (URN)10.1063/1.1864852 (DOI)
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2013-11-25
2. Probing the potential energy surface by highresolution x-ray absorption spectroscopy: The umbrella motion of the coreexcited CH3 free radical
Open this publication in new window or tab >>Probing the potential energy surface by highresolution x-ray absorption spectroscopy: The umbrella motion of the coreexcited CH3 free radical
Show others...
2007 (English)In: Physical Review. A, ISSN 1050-2947, Vol. 76, no 2, 124305- p.Article in journal (Refereed) Published
Abstract [en]

A detailed study of the umbrellalike vibration in inner-shell spectroscopy is presented. The high-resolution x-ray absorption spectrum for the lowest lying core excitation of the CH3 free radical was recorded. High quality potential energy surfaces (PES) for the initial and final states of the transition were calculated as a function of the symmetrical stretching and the umbrella deformation coordinates. The strong anharmonicity along the umbrella coordinate in the double-well region of the PES of the core excited state has a strong effect on the bending vibrational progressions. The excellent agreement between the experiment and theory allows an accurate spectroscopic characterization of the vibrational structure of the electronic transition, and the estimation of the umbrella inversion time of 149  fs.

Keyword
free radicals, molecular configurations, optical rotation, organic compounds, potential energy surfaces, vibrational states, X-ray absorption spectra
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-12686 (URN)10.1103/PhysRevA.76.022509 (DOI)
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2009-04-23Bibliographically approved
3. The umbrella motion of core-excited CH3 and CD3 methyl radicals
Open this publication in new window or tab >>The umbrella motion of core-excited CH3 and CD3 methyl radicals
Show others...
2008 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 128, no 4, 044302-1-044302-11 p.Article in journal (Refereed) Published
Abstract [en]

An accurate experimental and theoretical study of the lowest core excitationof CH3 and CD3 methyl radicals is presented. The complexvibrational structure of the lowest band of the x-ray absorptionspectrum (XAS) is due to the large variation of themolecular geometry, which is planar in the ground state andpyramidal in the core-excited state. The XAS spectra of thetwo radicals were recorded at high resolution and assigned bytheoretical simulations of the spectra, taking into account the couplingof symmetrical stretching and symmetrical bending (umbrellalike) deformations of theradicals. An excellent agreement between experimental and theoretical spectral profilesallowed us to accurately characterize the vibrational structure of theelectronic transition. The similarities, as well as the differences, ofthe peculiar vibrational progression observed for the two radicals areexplained by the strong anharmonicity along the umbrella coordinate andby the isotopic variation, leading to a different probing ofthe double-well potential energy surface of the core excited stateduring the nuclear motion.

Place, publisher, year, edition, pages
College Park, MD United States: American Institute of Physics (AIP), 2008
Keyword
excited states, free radicals, ground states, molecular configurations, organic compounds, potential energy surfaces, vibrational states, X-ray scattering
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12687 (URN)10.1063/1.2822246 (DOI)000252821200025 ()
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2017-12-14Bibliographically approved
4. Relativistic four-component static-exchange approximation for core-excitation processes in molecules
Open this publication in new window or tab >>Relativistic four-component static-exchange approximation for core-excitation processes in molecules
2006 (English)In: Physical review A, ISSN 1050-2947, Vol. 73, no 2, 022501- p.Article in journal (Refereed) Published
Abstract [en]

A generalization of the static-exchange approximation for core-electron spectroscopies to the relativistic four-component realm is presented. The initial state is a Kramers restricted Hartree-Fock state and the final state is formed as the configuration-interaction single excited state, based on the average of configurations for (n–1) electrons in n near-degenerate core orbitals for the reference ionic state. It is demonstrated that the static-exchange Hamiltonian can be made real by considering a set of time-reversal symmetric electron excitation operators. The static-exchange Hamiltonian is constructed at a cost that parallels a single Fock matrix construction in a quaternion framework that fully exploits time-reversal and spatial symmetries for the D2h point group and subgroups. The K- and L-edge absorption spectra of H2S are used to illustrate the methodology. The calculations adopt the Dirac-Coulomb Hamiltonian, but the theory is open ended toward improvements in the electron-electron interaction operator. It is demonstrated that relativistic effects are substantial for the L-edge spectrum of sulfur, and substantial deviations from the statistical 2:1 spin-orbit splitting of the intensity distribution are found. The average ratio in the mixed region is 1.54 at the present level of theory.

Keyword
hydrogen compounds, relativistic corrections, configuration interactions, HF calculations, excited states, spin-orbit interactions
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12688 (URN)10.1103/PhysRevA.73.022501 (DOI)
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2013-11-25
5. Resonant LII;III x-ray raman scattering from HCl
Open this publication in new window or tab >>Resonant LII;III x-ray raman scattering from HCl
Show others...
2006 (English)In: Physical Review A, ISSN 1050-2947, Vol. 74, no 6, 062512- p.Article in journal (Refereed) Published
Abstract [en]

We have studied the spectral features of Cl LII,III resonant x-ray Raman scattering of HCl molecules in gas phase both experimentally and theoretically. The theory, formulated in the intermediate-coupling scheme, takes into account the spin-orbital and molecular-field splittings in the Cl 2p shells, as well as the Coulomb interaction of the core hole with unoccupied molecular orbitals. Experiment and theory display nondispersive dissociative peaks formed by decay transitions in both molecular and dissociative regions. The molecular and atomic peaks collapse in a single narrow resonance because the dissociative potentials of core-excited and final states are parallel to each other along the whole pathway of the nuclear wave packet.

Keyword
hydrogen compounds, X-ray spectra, Raman spectra, dissociation energies, spin-orbit interactions, excited states
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12689 (URN)10.1103/PhysRevA.74.062512 (DOI)
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2009-06-05
6. Characterization of the chemisorption of methylsilane on a Au(1,1,1) surface from the silicon K- and L-edge spectra: a theoretical study using the four-component static exchange approximation
Open this publication in new window or tab >>Characterization of the chemisorption of methylsilane on a Au(1,1,1) surface from the silicon K- and L-edge spectra: a theoretical study using the four-component static exchange approximation
2005 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, 13846-13850 p.Article in journal (Refereed) Published
Abstract [en]

X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectra (NEXAFS) of methylsilane, isolated and chemisorbed to a Au(1,1,1) surface, are determined in the fully relativistic four-component static exchange approximation¯both the K- and the L-edge of silicon are addressed in this investigation. In the fully chemisorbed structure, three H(Si) atoms have been cleaved off when Si binds in the hollow site of Au forming three Si−Au bonds of normal length. As due to the tri-coordinated chemisorption, the onsets of the K- and L-edge NEXAFS absorption bands occur some 2.0 and 2.5 eV lower in energy, respectively. The spin−orbit splittings in the silicon 2p-shell are not significantly changed due to adsorption. A partly chemisorbed methylsilane with only one H(Si) bond cleaved was also studied, and it is shown that the polarization dependence in the surface spectra contains details that can be used experimentally to identify the surface coordination of silicon. The red-shifts in the XPS silicon 1s (2p) spectra upon surface binding are 0.95 (0.65) and 1.15 (0.83) eV for the mono- and tricoordinated system, respectively.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12690 (URN)10.1021/jp0717084 (DOI)
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2017-12-14
7. X-ray absorption spectra from the resonantconvergent first-order polarization propagator approach
Open this publication in new window or tab >>X-ray absorption spectra from the resonantconvergent first-order polarization propagator approach
2006 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 74, no 4, 042722- p.Article in journal (Refereed) Published
Abstract [en]

The one-photon absorption cross sections of molecular systems have been determined in the high-energy region from the imaginary part of the electric dipole polarizability tensor. In contrast to commonly adopted state-specific methodologies, the complex polarization propagator approach does not require explicit consideration of the excited states and it is open-ended towards multiphoton absorption. It is shown that the electronic relaxation in the core-hole state is well accounted for in the present approach with use of standard density-functional based electronic structure methods. Sample calculations are presented of the K-edge x-ray absorption spectra for H2O, CO, C4H4N, and C6H6.

Keyword
water, carbon compounds, organic compounds, X-ray absorption spectra, molecular moments, polarisability, electric moments, excited states, multiphoton spectra, density functional theory
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12691 (URN)10.1103/PhysRevA.74.042722 (DOI)
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2017-12-14
8. Polarization propagator for x-ray spectra
Open this publication in new window or tab >>Polarization propagator for x-ray spectra
2006 (English)In: Physical Review Letters, ISSN 1050-2947, Vol. 97, no 14, 143001- p.Article in journal (Refereed) Published
Abstract [en]

A polarization propagator for x-ray spectra is outlined and implemented in density functional theory. It rests on a formulation of a resonant-convergent first-order polarization propagator approach which makes it possible to directly calculate the x-ray absorption cross section at a particular frequency without explicitly addressing the excited states. The quality of the predicted x-ray spectrum relates only to the type of density functional applied without any separate treatment of dynamical relaxation effects.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12692 (URN)10.1103/PhysRevLett.97.143001 (DOI)
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2009-05-11
9. Self-interaction-corrected time-dependent density functional theory calculations of x-ray absorption spectra
Open this publication in new window or tab >>Self-interaction-corrected time-dependent density functional theory calculations of x-ray absorption spectra
Show others...
2007 (English)In: Physical Review A, ISSN 1050-2947, Vol. 76, no 2, 022506- p.Article in journal (Refereed) Published
Abstract [en]

We outline an approach within time-dependent density functional theory that predicts x-ray spectra on an absolute scale. The approach rests on a recent formulation of the resonant-convergent first-order polarization propagator [P. Norman et al., J. Chem. Phys. 123, 194103 (2005)] and corrects for the self-interaction energy of the core orbital. This polarization propagator approach makes it possible to directly calculate the x-ray absorption cross section at a particular frequency without explicitly addressing the excited-state spectrum. The self-interaction correction for the employed density functional accounts for an energy shift of the spectrum, and fully correlated absolute-scale x-ray spectra are thereby obtained based solely on optimization of the electronic ground state. The procedure is benchmarked against experimental spectra of a set of small organic molecules at the carbon, nitrogen, and oxygen K edges.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12693 (URN)10.1103/PhysRevA.76.022506 (DOI)
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2009-05-15
10. Near-edge X-ray absorption and natural circular dichroism spectra of L-alanine: a theoretical study based on the complex polarization propagator approach
Open this publication in new window or tab >>Near-edge X-ray absorption and natural circular dichroism spectra of L-alanine: a theoretical study based on the complex polarization propagator approach
2007 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, no 16, 165104- p.Article in journal (Refereed) Published
Abstract [en]

The complex polarization propagator method [J. Chem. Phys. 123, 194103 (2005)] has been employed in conjunction with density functional theory and gauge-including atomic orbitals in order to determine the near-edge x-ray absorption and natural circular dichroism spectra of L-alanine in its neutral and zwitterionic forms. Results are presented for the K-edges of carbon, nitrogen, and oxygen. In contrast to traditional methods, the proposed approach enables a direct determination ofspectra at an arbitrary frequency instead of focusing on the rotatory strengths for individual electronic transitions. The propagator includes a complete set ofand allows for full core-hole relaxation. The theoretical spectrum at the nitrogen K-edge of the zwitterion compares well with the experimental spectrum. the nonredundant electron-transfer operators

Keyword
X-ray absorption near edge structure, absorption spectra, dichroism, polarization spectroscopy, density functionals, atomic orbitals
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12724 (URN)10.1063/1.2800024 (DOI)
Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2017-12-14
11. Four-component Hartree–Fock calculations of magnetic-field induced circular birefringence—Faraday effect—in noble gases and dihalogens
Open this publication in new window or tab >>Four-component Hartree–Fock calculations of magnetic-field induced circular birefringence—Faraday effect—in noble gases and dihalogens
2005 (English)In: The Journal of Chemical Physics, ISSN 1050-2947, Vol. 122, 074321- p.Article in journal (Refereed) Published
Abstract [en]

Theeffects of relativity on the magnetic-field induced circular birefringence, orFaraday effect, in He, Ne, Ar, Xe, Rn, F2, Cl2,Br2, and I2 have been determined at the four-component Hartree–Focklevel of theory. A measure of the birefringence is givenby the Verdet constant, which is a third-order molecular propertyand thus relates to quadratic response functions. A fully analyticalnonlinear polarization propagator approach is employed. The results are gaugeinvariant as a consequence of the spatial symmetries in themolecular systems. The calculations include electronic as well as vibrationalcontributions to the property. Comparison with experiment is made forHe, Ne, Ar, Xe, and Cl2, and, apart from neon,the theoretical values of the Verdet constant are within 10%of the experimental ones. The inclusion of nonrelativistically spin-forbidden excitationsin the propagator parametrization has significant effects on the dispersionin general, but such effects are in the general caselargely explained by the use of a resonant-divergent propagator theory.In the present work we do, however, observe noticeable relativisticcorrections to the Verdet constant in the off-resonant regions forsystems with light elements (F2 and Cl2), and nonrelativistic resultsfor the Verdet constant of Br2 are in error by25% in the low-frequency region. ©2005 American Institute of Physics.

Keyword
HF calculations, birefringence, helium, neon, argon, xenon, radon, fluorine, chlorine, bromine, iodine, Faraday effect, polarisation, relativistic corrections, vibrational states, excited states, resonant states, magnetic fields
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12695 (URN)10.1063/1.1849167 (DOI)
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2013-11-25
12. The molecular electric quadrupole moment and electric field gradient induced birefringence (Buckingham effect) of Cl2
Open this publication in new window or tab >>The molecular electric quadrupole moment and electric field gradient induced birefringence (Buckingham effect) of Cl2
2004 (English)In: Journal of Computational Methods in Sciences and Engineering, ISSN 1472-7978, Vol. 4, no 3, 365-380 p.Article in journal (Refereed) Published
Abstract [en]

An ab initio investigation of the molecular properties rationalizing the electric-field-gradient induced birefringence (Buckingham effect) for Cl_2 is presented. The quadrupole moment is determined using hierarchies of basis sets and wavefunction models. The electric dipole polarizability, the dipole - dipole - quadrupole and dipole - dipole - magnetic dipole hyperpolarizabilities are determined exploiting a Coupled Cluster Singles and Doubles (CCSD) response approach. The properties are zero-point vibrationally averaged, and the contribution of excited ro-vibrational states accounted for. To this end, the interatomic ^1Σ_g^+ ground state potential has been computed at CCSD plus perturbative triples - CCSD(T) - level employing a large augmented correlation consistent basis set. The effect of relativity is estimated at the Dirac-Hartree-Fock level. Our best value for the quadrupole moment of Cl_2 is (2.327 ± 0.010) au and it is in excellent agreement with experiment which, after revision and dependent on the procedure employed for correcting the original estimate of (2.24 ± 0.04) au of Graham et al., [Mol. Phys., 93, 49, (1998)], ranges from (2.31 ± 0.04) au to (2.36 ± 0.04) au.

Keyword
molecular quadrupole moment, birefringence, electric field gradient, electric dipole (hyper)polarizabilities, coupled cluster theory, relativistic effects, molecular vibrations
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12696 (URN)
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2013-11-25
13. On the evaluation of quadratic response functions at the four-component Hartree-Fock level: Nonlinear polarization and two-photon absorption in bromo- and iodobenzen
Open this publication in new window or tab >>On the evaluation of quadratic response functions at the four-component Hartree-Fock level: Nonlinear polarization and two-photon absorption in bromo- and iodobenzen
2006 (English)In: The Journal of Chemical Physics, ISSN 0021-9606, Vol. 124, no 21, 214311- p.Article in journal (Refereed) Published
Abstract [en]

The nonlinear polarization and two-photon absorption parameters have been determined for dibromo- and di-iodobenzene in their meta- and ortho-conformations and with relativistic effects accounted for to a varying degree. By exclusion of small component integrals in the calculations of the first-order hyperpolarizability, results within 1% of fully relativistic four-component Hartree-Fock values are obtained at a cost of 8.7 times the corresponding nonrelativistic calculations. It is shown that the nonlinear absorption in bromobenzene (and even more so in iodobenzene) is broad banded due to spin-orbit interactions among the excited states, and nonrelativistic and scalar relativistic calculations are not to be used in this case.

Keyword
organic compounds, HF calculations, two-photon processes, relativistic corrections, polarisability, spin-orbit interactions, excited states
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13999 (URN)10.1063/1.2204604 (DOI)
Available from: 2006-10-05 Created: 2006-10-05 Last updated: 2009-05-18

Open Access in DiVA

cover(576 kB)123 downloads
File information
File name COVER01.pdfFile size 576 kBChecksum MD5
0e4cfa77c1104427e6e354666852e0f4199a5a214ba0820c4febeee91add523508fccbad
Type coverMimetype application/pdf
fulltext(4693 kB)803 downloads
File information
File name FULLTEXT01.pdfFile size 4693 kBChecksum MD5
712224b452a73ea9601e543f9fed12519e3e84664eb4e1f2a714f0f5cb650815d1463060
Type fulltextMimetype application/pdf

Authority records BETA

Ekström, Ulf

Search in DiVA

By author/editor
Ekström, Ulf
By organisation
Computational Physics The Institute of Technology
Other Physics Topics

Search outside of DiVA

GoogleGoogle Scholar
Total: 803 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 2026 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf