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X-absorption spectra of water within a plane-wave Car-Parrinello molecular dynamics framework
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
2004 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 20, 10065-10075 p.Article in journal (Refereed) Submitted
Abstract [en]

We describe the implementation of a simple technique to simulate core-level spectra within the Car-Parrinello plane-waves molecular dynamics framework. The x-ray absorption (XA) spectra are generated using the transition potential technique with the effect of the core hole included through a specifically developed pseudopotential for the core-excited atom. Despite the lack of 1s core orbitals in the pseudopotential treatment, the required transition moments are accurately calculated without reconstruction of the all-electron orbitals. The method is applied to the oxygen XA spectra of water in its various aggregation states, but it is transferable to any first-row element. The computed spectra are compared favorably with the results from all-electron cluster calculations, as well as with experimental data. The periodicity of the plane-wave technique improves the description of condensed phases. The molecular dynamics simulation enables in principle a proper treatment of thermal effects and dynamical averaging in complex systems.

Place, publisher, year, edition, pages
American Institute of Physics , 2004. Vol. 121, no 20, 10065-10075 p.
Keyword [en]
X-ray absorption spectra, water, molecular dynamics method, core levels, pseudopotential methods, transition moments, molecular electronic states, APW calculations, spectroscopy computing
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-23408DOI: 10.1063/1.1807821OAI: oai:DiVA.org:su-23408DiVA: diva2:191963
Note
Part of urn:nbn:se:su:diva-286Available from: 2004-11-17 Created: 2004-11-17 Last updated: 2010-12-08Bibliographically approved
In thesis
1. Local Structure of Hydrogen-Bonded Liquids
Open this publication in new window or tab >>Local Structure of Hydrogen-Bonded Liquids
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ordinary yet unique, water is the substance on which life is based. Water seems, at first sight, to be a very simple molecule, consisting of two hydrogen atoms attached to one oxygen. Its small size belies the complexity of its action and its numerous anomalies, central to a broad class of important phenomena, ranging from global current circulation, terrestrial water and CO2 cycles to corrosion and wetting. The explanation of this complex behavior comes from water's unique ability to form extensive three-dimensional networks of hydrogen-bonds, whose nature and structures, in spite of a great deal of efforts involving a plethora of experimental and theoretical techniques, still lacks a complete scientific understanding.

This thesis is devoted to the study of the local structure of hydrogen-bonded liquids, with a particular emphasis on water, taking advantage of a combination of core-level spectroscopies and density functional theory spectra calculations. X-ray absorption, in particular, is found to be sensitive to the local hydrogen-bond environment, thus offering a very promising tool for spectroscopic identification of specific structural configurations in water, alcohols and aqueous solutions. More specifically, the characteristic spectroscopic signature of the broken hydrogen-bond at the hydrogen side is used to analyze the structure of bulk water, leading to the finding that most molecules are arranged in two hydrogen-bond configurations, in contrast to the picture provided by molecular dynamics simulations. At the liquid-vapor interface, an interplay of surface sensitive measurements and theoretical calculations enables us to distinguish a new interfacial species in equilibrium with the gas. In a similar approach the cluster form of the excess proton in highly concentrated acid solutions and the different coordination of methanol at the vacuum interface and in the bulk can also be clearly identified.

Finally the ability of core-level spectroscopies, aided by sophisticated density functional theory calculations, to directly probe the valence electronic structure of a system is used to observe the nature of the interaction between water molecules and solvated ions in solution. Water around transition metal ions is found to interact with the solute via orbital mixing with the metal d-orbitals. The hydrogen-bond between water molecules is explained in terms of electrostatic interactions enhanced by charge rehybridization in which charge transfer between connecting molecules is shown to be fundamental.

Place, publisher, year, edition, pages
Stockholm: Fysikum, 2004. 66 p.
Keyword
hydrogen-bond, water, ice, density functional theory, DFT, core-level spectroscopies, x-ray absorption
National Category
Physical Chemistry
Identifiers
urn:nbn:se:su:diva-286 (URN)91-7265-969-6 (ISBN)
Public defence
2004-12-08, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-11-17 Created: 2004-11-17Bibliographically approved

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