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Coupled-cluster response theory for near-edge x-ray-absorption fine structure of atoms and molecules
University of Aarhus.
University of Aarhus.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
2012 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 2, 022507- p.Article in journal (Refereed) Published
Abstract [en]

Based on an asymmetric Lanczos-chain subspace algorithm, damped coupled cluster linear response functions have been implemented for the hierarchy of coupled cluster (CC) models including CC with single excitations (CCS), CC2, CC with single and double excitations (CCSD), and CCSD with noniterative triple corrected excitation energies CCSDR(3). This work is a first step toward the extension of these theoretical electronic structure methods of well-established high accuracy in UV-vis absorption spectroscopies to applications concerned with x-ray radiation. From the imaginary part of the linear response function, the near K-edge x-ray absorption spectra of neon, water, and carbon monoxide are determined and compared with experiment. Results at the CCSD level show relative peak intensities in good agreement with experiment with discrepancies in transition energies due to incomplete treatment of electronic relaxation and correlation that amount to 1-2 eV. With inclusion of triple excitations, errors in energetics are less than 0.9 eV and thereby capturing 90%, 95%, and 98% of the relaxation-correlation energies for C, O, and Ne, respectively.

Place, publisher, year, edition, pages
American Physical Society , 2012. Vol. 85, no 2, 022507- p.
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-75466DOI: 10.1103/PhysRevA.85.022507ISI: 000300081800005OAI: diva2:507087
Funding Agencies|EU|254326|Swedish Research Council|621-2010-5014|National Supercomputer Centre (NSC), Sweden||Available from: 2012-03-02 Created: 2012-03-02 Last updated: 2013-12-02
In thesis
1. X-ray absorption spectroscopy through damped coupled cluster response theory
Open this publication in new window or tab >>X-ray absorption spectroscopy through damped coupled cluster response theory
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

For a fundamental understanding of the interaction of electromagnetic radiation and molecular materials, experimental measurements are to be combined with theoretical models. With this combination, materials can be characterized in terms of composition, structure, time-resolved chemical reactions, and other properties. This licentiate thesis deals with the development and evaluation of a theoretical method by which X-ray absorption spectra can be interpreted and predicted.

In X-ray absorption spectroscopy the photon energy is tuned such that core electrons are targeted and excited to bound states. Such core excitations exhibit strong relaxation eects, making theoretical considerations of the processes especially challenging. In order to meet these challenges, a damped formalism of the coupled cluster (CC) linear response function has been developed, and the performance of this approach evaluated. Amongst the quantum chemical methods available, CC stands out as perhaps the most accurate, with a systematic manner by which the correct physical description can be approached. Coupled with response theory, we thus have a reliable theoretical method in which relaxation eects are addressed by means of an accurate treatment of electron correlation.

By use of the hierarchy of CC approximations (CCS, CC2, CCSD, CCSDR(3)), it has been shown that the relaxation eects are accounted for by the inclusion of double and triple excitations in the CC excitation manifold. The performance of the methods for K-edge NEXAFS spectra for water, neon, carbon monoxide, ammonia, acetone, and a number of uorine-substituted ethenes has been investigated, and we observe relaxation eects amounting to 7–21 eV. The discrepancy in absolute energy for the most accurate calculations as compared to experiments are reported as 0.4–1.5 eV, and the means by which this can be decreased further are discussed. For relative energies, it has been demonstrated that CCSD yields excellent spectral features, while CC2 yields good agreement to experiments only for the most intense features. Comparisons have also been made to the more computationally viable method of density functional theory, for which spectral features are in excellent agreement with experiment.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 55 p.
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1625
National Category
Natural Sciences
urn:nbn:se:liu:diva-102177 (URN)10.3384/lic.diva-102177 (DOI)LIU-TEK-LIC-2013:59 (Local ID)978-91-7519-484-4 (print) (ISBN)LIU-TEK-LIC-2013:59 (Archive number)LIU-TEK-LIC-2013:59 (OAI)
2013-12-12, Nobel, B-huset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2013-12-02 Created: 2013-12-02 Last updated: 2013-12-05Bibliographically approved

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