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Near-edge X-ray absorption and natural circular dichroism spectra of L-alanine: a theoretical study based on the complex polarization propagator approach
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
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.
2007 (English)In: Journal of Chemical Physics, ISSN 0021-9606, 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

Place, publisher, year, edition, pages
2007. Vol. 127, no 16, 165104- p.
Keyword [en]
X-ray absorption near edge structure, absorption spectra, dichroism, polarization spectroscopy, density functionals, atomic orbitals
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-12724DOI: 10.1063/1.2800024OAI: oai:DiVA.org:liu-12724DiVA: diva2:16913
Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2009-05-04
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. Long-range intermolecular dispersion forces and circular dichroism spectra from first-principles calculations
Open this publication in new window or tab >>Long-range intermolecular dispersion forces and circular dichroism spectra from first-principles calculations
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work presents first-principles calculations of long-range intermolecular dispersion energies between two atoms or molecules and of electronic circular dichroism spectra of chiral molecules. The former is expressed in terms of the C6 dipole-dipole dispersion coefficients Δε, and the latter is given in terms of the extinction coefficient. In a series of publications, the complex linear polarization propagator method has been shown to be a powerful tool to provide accurate ab initio and first-principles density functional theory results. This was the case not only for the C6 dispersion coefficients but also for the electronic circular dichroism at an arbitrary wavelength ranging from the optical to the X-ray regions of the spectrum. The selected samples for the investigation of dispersion interactions in the electronic ground state are the noble gases, n-alkanes, polyacenes, azabenzenes, alkali-metal clusters, and C60. It is found that the values of C6 for the sodium-cluster-to-fullerene interactions are well within the error bars of the experiment. The proposed method can also be used to determine dispersion energies for species in their respective excited electronic states. The C6 dispersion coefficients for the first π → π* excited state of the azabenzene molecules have been obtained with the adopted method in the multiconfiguration self-consistent field approximation. The dispersion energy of the π → π* excited state is smaller than that of the ground state. It is found that the characteristic frequencies ω1 defined in the London approximation of n-alkanes vary in a narrow range which makes it possible to construct a simple structure-to-property relationship based on the number of π-bonds for the dispersion interaction in these saturated compounds. However, this simple approach is not applicable to the interactions of the π-conjugated systems since, depending on the systems, their characteristic frequencies ω1 can vary greatly. In addition, an accomplishment of calculations of the electronic circular dichroism spectra in the near-edge X-ray absorption has been demonstrated.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2007. 42 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1118
Keyword
van der Waals forces, dispersion forces, dispersion coefficients, polarizability, electronic circular dichroism
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-10151 (URN)978-91-85831-41-8 (ISBN)
Public defence
2007-10-02, Planck, Fysikhuset, Campus Valla, Linköping University, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2013-10-02

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Jiemchooroj, AuaypornEkström, UlfNorman, Patrick

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