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Ab Initio Calculations of X-ray Spectra: Atomic Multiplet and Molecular Orbital Effects in a Multiconfigurational SCF Approach to the L-Edge Spectra of Transition Metal Complexes
Stockholm University, Faculty of Science, Department of Physics.
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Number of Authors: 7
2012 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 3, no 23, 3565-3570 p.Article in journal (Refereed) Published
Abstract [en]

A new ab initio approach to the calculation of X-ray spectra is demonstrated. It combines a high-level quantum chemical description of the chemical interactions and local atomic multiplet effects. We show here calculated L-edge X-ray absorption (XA) and resonant inelastic X-ray scattering spectra for aqueous Ni2+ and XA spectra for a polypyridyl iron complex. Our quantum chemical calculations on a high level of accuracy in a post-Hartree–Fock framework give excellent agreement with experiment. This opens the door to reliable and detailed information on chemical interactions and the valence electronic structure in 3d transition-metal complexes also in transient excited electronic states. As we combine a molecular-orbital description with a proper treatment of local atomic electron correlation effects, our calculations uniquely allow, in particular, identifying the influence of interatomic chemical interactions versus intra-atomic correlations in the L-edge X-ray spectra.

Place, publisher, year, edition, pages
2012. Vol. 3, no 23, 3565-3570 p.
Keyword [en]
X-ray spectroscopy, spectrum simulations, resonant inelastic X-ray scattering, RASSCF calculations, transition metal ions
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-85227DOI: 10.1021/jz301479jISI: 000312170600029OAI: oai:DiVA.org:su-85227DiVA: diva2:583005
Funder
Swedish Research Council
Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Ab initio simulations of core level spectra: Towards an atomistic understanding of the dye-sensitized solar cell
Open this publication in new window or tab >>Ab initio simulations of core level spectra: Towards an atomistic understanding of the dye-sensitized solar cell
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The main focus of this thesis is ab initio modeling of core level spectra with a high-level quantum chemical description both of the chemical interactions and of local atomic multiplet effects. In particular, the combination of calculations and synchrotron-based core-level spectroscopy aims at understanding the local structure of the electronic valence in transition metal complexes, and the details of the solvation mechanisms of electrolyte solutions, systems relevant for the dye-sensitized solar cell. Configurational sampling in solution is included through molecular dynamics simulations.

Transition metal complexes are studied with x-ray absorption (XA) and resonant inelastic scattering (RIXS) spectroscopy, characterizing excited states with atomic site specificity. The theoretical multiconfigurational method, applying an active-space partitioning of the molecular orbitals (RASSCF), is used to assign the transitions observed in spectra of hydrated Ni2+ explicitly, including charge transfer and multiplet effects.

Furthermore, the solvent-induced binding energy properties of the I- and I3- anions in aqueous, ethanol, and acetonitrile solutions are analyzed using photoelectron spectroscopy (XPS). The study shows that specific ion–solvent interactions are important for the core-level binding energy shifts in solution. The special case with I3- dissolved in water, where hydrogen bonding causes breaking of the molecular symmetry, is treated and proves that the geometry changes influence the photoelectron spectrum of aqueous I3- directly.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2013. 31 p.
Keyword
multiconfigurational quantum chemistry, CASSCF calculations, core-level spectroscopy, x-ray photoelectron spectroscopy, x-ray absorption, resonant x-ray scattering, dye solar cells, transition metals
National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-93098 (URN)
Presentation
2013-09-23, FA31, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Available from: 2013-09-10 Created: 2013-09-02 Last updated: 2013-10-08Bibliographically approved
2. Structure and dynamics in solution – the core electron perspective
Open this publication in new window or tab >>Structure and dynamics in solution – the core electron perspective
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is based on theoretical studies of the molecular and electronic structure of solvated ions and molecules. Very detailed information of the system can be obtained from theoretical calculations, but a realistic model is dependent on an accurate computational method. Accurate calculations of core level electronic spectra, and evaluation of the modeling against experiments, are central parts of this work. The main tools used for characterization of the systems are high-level quantum chemistry and molecular dynamics simulations. 

Molecular components in solutions are involved in many key processes converting sunlight into chemical or electrical energy. Transition metal complexes, with their pronounced absorption in the visible light region of the electromagnetic spectrum, are core components in various energy conversion applications, and the iodide/triiodide redox couple is a commonly used electrolyte. The local structure of the electronic valence in transition metal complexes and the details of the solvation mechanisms of electrolyte solutions are investigated through the combination of computational modeling and core level spectroscopy. The studies of model systems show that interactions between the solute and solvent are important for the electronic structure, and knowledge of the details in model systems studied can be relevant for energy conversion applications. Furthermore, high-level quantum chemistry has been applied for interpreting time-resolved spectra, where the electronic structure of a metal complex is followed during a photoinduced chemical reaction in solution.

With advanced modeling in combination with recent experimental developments, more complex problems than previously addressed can be dissected.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2015. 64 p.
Keyword
quantum chemistry, RASSCF, molecular dynamics, x-ray spectroscopy, electrolyte solutions
National Category
Natural Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-119838 (URN)978-91-7649-258-1 (ISBN)
Public defence
2015-10-15, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 8: Manuscript.

Available from: 2015-09-23 Created: 2015-08-26 Last updated: 2015-09-11Bibliographically approved

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