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Relativistic four-component static-exchange approximation for core-excitation processes in molecules
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
Istituto per i Processi Chimico-Fisici, Area della Ricerca del C.N.R., Pisa, Italy.
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.

Place, publisher, year, edition, pages
2006. Vol. 73, no 2, 022501- p.
Keyword [en]
hydrogen compounds, relativistic corrections, configuration interactions, HF calculations, excited states, spin-orbit interactions
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-12688DOI: 10.1103/PhysRevA.73.022501OAI: oai:DiVA.org:liu-12688DiVA: diva2:16862
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2013-11-25
In thesis
1. Time-dependent molecular properties in the optical and x-ray regions
Open this publication in new window or tab >>Time-dependent molecular properties in the optical and x-ray regions
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
Quantum chemistry, molecular physics, x-ray spectroscopy, relativity
National Category
Other Physics Topics
Identifiers
urn:nbn:se:liu:diva-10125 (URN)978-91-85895-88-5 (ISBN)
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
2. Birefringences and X-ray absorption from relativistic and nonrelativistic quantum chemical methods
Open this publication in new window or tab >>Birefringences and X-ray absorption from relativistic and nonrelativistic quantum chemical methods
2005 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Application of quantum chemical methods for the prediction and interpretation of optical and X-ray experiments have been performed. X-ray absorption and X-ray photo-electron spectroscopy of pentacene in the gas phase has been studied using the static exchange approximation. A generalizat ion of the static exchange approximation, to the relativistic four-component realm is presented and applied to the H2S molecule. This generalization allows for a description of the effects the strong spin-orbit coupling in the core region of atoms. Two types of birefringences, Faraday effect and electric field gradient induced birefringence, a re calculated for small molecules in the gas phase, and the effects of relativity are considered for these nonlinear optical properties.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2005. 40 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1211
Series
LIU-TEK-LIC, 66
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-31976 (URN)17818 (Local ID)91-8545-772-8 (ISBN)17818 (Archive number)17818 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-11-25

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Ekström, UlfNorman, Patrick

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