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X-ray absorption spectroscopy through damped coupled cluster response theory
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
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.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1625
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-102177DOI: 10.3384/lic.diva-102177Local ID: LIU-TEK-LIC-2013:59ISBN: 978-91-7519-484-4 (print)OAI: oai:DiVA.org:liu-102177DiVA: diva2:668866
Presentation
2013-12-12, Nobel, B-huset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-12-02 Created: 2013-12-02 Last updated: 2013-12-05Bibliographically approved
List of papers
1. Coupled-cluster response theory for near-edge x-ray-absorption fine structure of atoms and molecules
Open this publication in new window or tab >>Coupled-cluster response theory for near-edge x-ray-absorption fine structure of atoms and molecules
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
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-75466 (URN)10.1103/PhysRevA.85.022507 (DOI)000300081800005 ()
Note
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: 2017-12-07
2. Asymmetric-Lanczos-Chain-Driven Implementation of Electronic Resonance Convergent Coupled-Cluster Linear Response Theory
Open this publication in new window or tab >>Asymmetric-Lanczos-Chain-Driven Implementation of Electronic Resonance Convergent Coupled-Cluster Linear Response Theory
2012 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 8, no 5, 1616-1628 p.Article in journal (Refereed) Published
Abstract [en]

We present an implementation of the damped coupled-cluster linear response function based on an asymmetric Lanczos chain algorithm for the hierarchy of coupled-cluster approximations CCS (coupled-cluster singles), CC2 (coupled. cluster singles and approximate doubles), and CCSD (coupled-cluster singles and doubles). Triple corrections to the excitation energies can be included via the CCSDR(3) (coupled-cluster singles and doubles with noniterative-triples-corrected excitation energies) approximation. The performance and some of the potentialities of the approach are investigated in calculations of the visible/ultraviolet absorption spectrum and the dispersion of the real polarizability in near-resonant regions of pyrimidine, the near-edge absorption fine structure (NEXAFS) of ammonia, and the direct determination of the C-6 dipole-dipole dispersion coefficient of the benzene dimer.

Place, publisher, year, edition, pages
American Chemical Society, 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-77865 (URN)10.1021/ct200919e (DOI)000303628400011 ()
Note
Funding Agencies|FP7-PEOPLE-2009-IEF|254326|Swedish Research Council|621-2010-S014|National Supercomputer Centre (NSC), Sweden||Available from: 2012-05-31 Created: 2012-05-31 Last updated: 2017-12-07
3. Carbon X-ray absorption spectra of fluoroethenes and acetone: A study at the coupled cluster, density functional, and static-exchange levels of theory
Open this publication in new window or tab >>Carbon X-ray absorption spectra of fluoroethenes and acetone: A study at the coupled cluster, density functional, and static-exchange levels of theory
2013 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 12Article in journal (Refereed) Published
Abstract [en]

Near carbon K-edge X-ray absorption fine structure spectra of a series of fluorine-substituted ethenes and acetone have been studied using coupled cluster and density functional theory (DFT) polarization propagator methods, as well as the static-exchange (STEX) approach. With the complex polarization propagator (CPP) implemented in coupled cluster theory, relaxation effects following the excitation of core electrons are accounted for in terms of electron correlation, enabling a systematic convergence of these effects with respect to electron excitations in the cluster operator. Coupled cluster results have been used as benchmarks for the assessment of propagator methods in DFT as well as the state-specific static-exchange approach. Calculations on ethene and 1,1-difluoroethene illustrate the possibility of using nonrelativistic coupled cluster singles and doubles (CCSD) with additional effects of electron correlation and relativity added as scalar shifts in energetics. It has been demonstrated that CPP spectra obtained with coupled cluster singles and approximate doubles (CC2), CCSD, and DFT (with a Coulomb attenuated exchange-correlation functional) yield excellent predictions of chemical shifts for vinylfluoride, 1,1-difluoroethene, trifluoroethene, as well as good spectral features for acetone in the case of CCSD and DFT. Following this, CPP-DFT is considered to be a viable option for the calculation of X-ray absorption spectra of larger pi-conjugated systems, and CC2 is deemed applicable for chemical shifts but not for studies of fine structure features. The CCSD method as well as the more approximate CC2 method are shown to yield spectral features relating to pi*-resonances in good agreement with experiment, not only for the aforementioned molecules but also for ethene, cis-1,2-difluoroethene, and tetrafluoroethene. The STEX approach is shown to underestimate pi*-peak separations due to spectral compressions, a characteristic which is inherent to this method.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-92613 (URN)10.1063/1.4795835 (DOI)000316969500078 ()
Note

Funding Agencies|Swedish Research Council|621-2010-5014|EU|254326|Supercomputer Centre (NSC), Sweden||

Available from: 2013-05-16 Created: 2013-05-14 Last updated: 2017-12-06

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