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Semi-classical description of nuclear dynamics in x-ray emission of water
Stockholm University, Faculty of Science, Department of Physics. (Kvantkemi)
Stockholm University, Faculty of Science, Department of Physics. (Kvantkemi)
Stockholm University, Faculty of Science, Department of Physics. (Kvantkemi)
2010 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 82, no 24, 245115- p.Article in journal (Refereed) Published
Abstract [en]

In this article we present a semi-classical approximation to the Kramers-Heisenberg formula for calculating x-ray emission (XES) spectra, including vibrational effects. We compare the method to the quantum Kramers-Heisenberg formula for a test system consisting of a model water dimer where the hydrogen-bond donor is core-ionized and obtain excellent agreement. In the semi-classical approach we average spectra from classical trajectories where the core-hole-induced dynamics is performed with initial conditions sampling the quantum zero-point position and momentum probability distributions in the O-H vibration. We find very similar time-evolution of the squared quantum wave packet compared to the probability distribution under classical dynamics until the proton interacts with the next water. We compare our semi-classical approach with other methods to compute the XES spectra of water that have been used in the past and conclude that our approach gives superior results while requiring the same computational effort.

Place, publisher, year, edition, pages
2010. Vol. 82, no 24, 245115- p.
National Category
Other Chemistry Topics
Research subject
Quantum Chemistry
Identifiers
URN: urn:nbn:se:su:diva-47120DOI: 10.1103/PhysRevB.82.245115OAI: oai:DiVA.org:su-47120DiVA: diva2:373042
Available from: 2010-11-29 Created: 2010-11-29 Last updated: 2017-12-12Bibliographically approved
In thesis
1. 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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