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OD vibrations and hydration structure in an Al3+(aq) solution from a Car-Parrinello Molecular Dynamics Simulation
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
2006 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 124, no 10, 104501- p.Article in journal (Refereed) Published
Abstract [en]

The optimized geometry, energetics, and vibrational properties of Al(D2O) clusters, with n=1,2,4, and 6, have been studied using plane waves, different local basis sets, different methodologies [density-functional theory, MP2, CCSD(T)], and different functionals (BLYP, PBE). Moreover, Car-Parrinello molecular-dynamics (MD) simulations using the BLYP functional, plane waves, and the Vanderbilt ultrasoft pseudopotentials have been performed for an aqueous Al3+ solution with 1 ion and 32 D2O molecules in a periodic box at room temperature, studied for 10 ps. The cluster calculations were performed to pinpoint possible shortcomings of the electronic structure description used in the Car-Parinello MD (CPMD) simulation. For the clusters, the hydration structure and interaction energies calculated with the `BLYP/plane-wave' approach agree well with high-level ab initio methods but the exchange-correlation functional introduces errors in the OD stretching frequencies (both in the absolute values and in the ion-induced shifts). For the aqueous solution, the CPMD simulation yields structural properties in good agreement with experimental data. The CPMD-simulated OD stretching vibrational band for the first-shell water molecules around Al3+ is strongly downshifted by the influence of the ion and is compared with experimental data from the literature. To make such a comparison meaningful, the influences of a number of systematic effects have been addressed, such as the exchange-correlation functional, the fictitious electron mass, anharmonicity effects, and the small box size in the simulation. Each of these factors (except the last one) is found to affect the OD frequency by 100 cm–1 or more. The final "corrected" frequencies agree with experiment within ~30 cm–1 for bulk water but are too little downshifted for the first-shell Al3+(aq) water molecules (by ~200 cm–1).

Place, publisher, year, edition, pages
2006. Vol. 124, no 10, 104501- p.
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-92891DOI: 10.1063/1.2131062OAI: oai:DiVA.org:uu-92891DiVA: diva2:166204
Available from: 2005-04-07 Created: 2005-04-07 Last updated: 2013-09-20Bibliographically approved
In thesis
1. Classical and Car-Parrinello Molecular Dynamics Simulations of Polyvalent Metal Ions in Water
Open this publication in new window or tab >>Classical and Car-Parrinello Molecular Dynamics Simulations of Polyvalent Metal Ions in Water
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aqueous solvation of metal ions is one of the long-standing and complex problems in chemistry, with implications for and applications in a broad range of biochemical and electrochemical systems, where water is the all-pervasive medium.

This thesis describes computer simulations of Al3+(aq), Fe2+(aq), Fe3+(aq) and Cu2+(aq). Various aspects of the solvation of these polyvalent metal ions in water are addressed, at different levels of theory, using Car-Parrinello molecular dynamics, classical molecular dynamics and quantum-mechanical cluster calculations. Polyvalent metal ions are particularly interesting because of their large influence on the solvent structure, dynamics and thermodynamics, as well as on the properties of the individual solvent molecules. Polyvalent metal ions in aqueous solution also constitute a challenging subject for computer simulations since a sophisticated interaction model is needed to incorporate the large many-body effects.

All the ion-water coordination figures in this thesis are octahedral, except in the Cu2+(aq) solution, where the ion is penta-coordinated with four equatorial neighbours in a plane and one axial neighbour located ~0.45 Å further out from the ion. The equatorial ion-water bonds have covalent character, while the axial water molecule is only electrostatically bound. For all the ions, the OD stretching frequencies of the first-shell water molecules are much more downshifted than in liquid water. In the case of Cu2+(aq), however, only the OD frequencies of the equatorial water molecules are downshifted with respect to bulk water whereas the OD frequencies of the axial water molecule are slightly upshifted.

Various limitations of the Car-Parrinello molecular dynamics simulations have been explored and compared, such as finite system-size effects and shortcomings in the electronic structure calculations. The Car-Parrinello simulations are found to give reasonable descriptions of the polyvalent metal ions in aqueous solution.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. vi+39 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 38
Keyword
Inorganic chemistry, Car-Parrinello molecular dynamics simulations, ab initio calculations, ion, copper, aluminium, metal ion, water, aqueous solution, solvation, Oorganisk kemi
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-5742 (URN)91-554-6211-1 (ISBN)
Public defence
2005-04-29, Polhemsalen, The Ångstrom Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2005-04-07 Created: 2005-04-07Bibliographically approved

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Spångberg, DanielHermansson, Kersti

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