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Theoretical Approximations to X-ray Absorption Spectroscopy of Liquid Water and Ice
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
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2010 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 177, no 2-3, 135-157 p.Article in journal (Refereed) Published
Abstract [en]

We review methods to compute x-ray absorption spectra (XAS) with special focus on the transition potential approach of Triguero et al. [Phys. Rev. B 58, 8097 (1998)] and its application to calculations on water in condensed phase. We discuss the absolute energy scale, functional dependence, broadening versus sampling of intra- and intermolecular vibrational modes, treatment of the continuum, cluster size convergence as well as compare with periodic calculations and with experiment; periodic and cluster model calculations are found to agree very closely in the relevant near-edge region although neither reproduces the pre-edge and main-edge features in the experimental spectra of thin ice films. The real space grid representation of the wave function in the periodic calculations allows a more extended energy range to be described and we find satisfactory agreement with experiment for higher energy continuum resonances. Two proposed alternative approaches using either the potential from a full core-hole (FCH) or the full core-hole with an excited electron in the lowest state (XCH) are shown to lead to spectra that deviate significantly from experiment.

Place, publisher, year, edition, pages
2010. Vol. 177, no 2-3, 135-157 p.
Keyword [en]
X-ray absorption spectroscopy; DFT; NEXAFS; Water structure; Transition-potential
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:su:diva-31447DOI: 10.1016/j.elspec.2010.02.004ISI: 000277949100007OAI: oai:DiVA.org:su-31447DiVA: diva2:277036
Available from: 2009-11-13 Created: 2009-11-13 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Structure Modeling with X-ray Absorption and Reverse Monte Carlo: Applications to Water
Open this publication in new window or tab >>Structure Modeling with X-ray Absorption and Reverse Monte Carlo: Applications to Water
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Water is an important substance. It is part of us, of our environment, and is a fundamental prerequisite for the existence of life as we know it. The structure of water is still, after over 100 years of research on the subject, however under debate. In this thesis x-ray absorption spectroscopy (XAS) and reverse Monte Carlo (RMC) modeling are used to search for structural solutions of water consistent with many different experimental data sets, with emphasis on the combination of different experimental techniques for a reliable structure determination. Neutron and x-ray diffraction are analyzed in combination with the more recent synchrotron radiation based XAS. Geometrical criteria for H-bonding are implemented in RMC to drive the fits and allow to evaluate differently H-bonded structure models against the data. It is shown that the available diffraction data put little constraints on the type of H-bond topology or O-O-O tetrahedrality for the structure of liquid water. It is also demonstrated that classical MD simulations, using some of the most common interaction potentials for water, give rise to O-O and O-H pair-correlation functions with too sharp first peaks at too short distances to be in agreement with diffraction, and furthermore that requiring a large fraction of broken H-bonds is not in itself enough for a structure model to reproduce the experimental XAS. A contribution to the theoretical description of XAS is made by an in-depth investigation of important technical aspects of the TP-DFT spectrum calculations. A novel approach to RMC, applicable also to data that require a significant amount of computer time to evaluate, is developed which makes use of pre-computed properties from a large set of local geometries allowing RMC simulations directly on data from core-level spectroscopies such as XAS.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2009. 83 p.
Keyword
water structure, x-ray absorption, spectroscopy, diffraction, reverse monte carlo, XAS, EXAFS, XANES, RMC, TP-DFT spectrum calculations
National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-31475 (URN)978-91-7155-972-2 (ISBN)
Public defence
2009-12-11, FB53 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 4, 5 and 6: SubmittedAvailable from: 2009-11-19 Created: 2009-11-16 Last updated: 2011-04-26Bibliographically approved
2. Theoretical modeling of x-ray and vibrational spectroscopies applied to liquid water and surface adsorbates
Open this publication in new window or tab >>Theoretical modeling of x-ray and vibrational spectroscopies applied to liquid water and surface adsorbates
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents results of theoretical modeling of x-ray and vibrational spectroscopies applied to liquid water and to CO adsorbed on a Ni(100) surface. The Reverse Monte Carlo method is used to search for  water structures that reproduce diffraction, IR/Raman and x-ray absorption by fitting them to experimental data and imposed constraints. Some of the structures are created to have a large fraction of broken hydrogen bonds because recent x-ray absorption and emission studies have been seen to support the existence of such structures. In the fitting procedure a fast way of computing the IR/Raman spectrum for an isolated OH stretch is used, where the frequency is represented by the electric field projected in the direction of the stretch coordinate. This method is critically evaluated by comparing it to quantum chemical cluster calculations. Furthermore, the x-ray emission spectrum of water is investigated, the modeling of which is complicated by the necessity of including vibrational effects in the spectrum calculations due to a dissociative intermediate state. Based on the Kramers-Heisenberg formula a new semi-classical method is developed to include vibrational effects in x-ray emission calculations. The method is seen to work very well for a one-dimensional test system. Moreover, x-ray absorption and emission are implemented in a periodic Density Functional Theory code which is applied to ice and to the surface adsorbate system CO on Ni(100).

Abstract [sv]

Den här avhandlingen presenterar resultat av teoretisk modellering av röntgen- och vibrationella spektroskopier applicerade på flytande vatten och på CO adsorberat på en Ni(100) -yta. Reverse Monte Carlo-metoden används till att söka efter vattenstrukturer som reproducerar diffraktion, IR/Raman, röntgenabsorption och emission genom att anpassa strukturerna till experimentella data samt till pålagda restriktionsvillkor. Vissa av strukturerna är skapade så att de har en stor andel brutna vätebindningar eftersom nya röntgenabsorptions- och emissionsexperiment har setts stödja förekomsten av sådana strukturer. I anpassningsprocessen används en metod för att snabbt beräkna IR/Raman-spektrum för en isolerad OH-stretch, där frekvensen representeras av det elektriska fältet projicerat i stretch-koordinatens riktning.Vi utvärderar kritiskt denna metod genom att jämföra den med kvantkemiska klusterberäkningar. Vidare undersöks vattens röntgenemissionsspektrum, vars modellering kompliceras av nödvändigheten att inkludera vibrationella effekter i spektrumberäkningarna på grund av ett dissociativt intermediärt tillstånd. Baserat på Kramers-Heisenbergformeln utvecklas en ny semiklassisk metod som inkluderar vibrationella effekter. Metoden visar sig fungera mycket väl för ett endimensionellt testsystem. Dessutom implementerar vi röntgenabsorption och emission i en periodisk Täthetsfunktionalteorikod som vi sedan applicerar  på is och på ett ytadsorbatsystem: CO på Ni(100).

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2010. 61 p.
Keyword
water, XAS, XES, IR, Raman
National Category
Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-38868 (URN)978-91-7447-096-3 (ISBN)
Public defence
2010-06-04, sal FR4, 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 4: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript.Available from: 2010-05-11 Created: 2010-05-03 Last updated: 2011-11-14Bibliographically approved

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Leetmaa, MikaelLjungberg, MathiasLyubartsev, AlexanderNilsson, AndersPettersson, Lars G.M.
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