Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 33: Methods: Electronic structure theory II
O 33.4: Vortrag
Mittwoch, 25. März 2009, 11:15–11:30, SCH A316
On the accuracy of DFT exchange-correlation functionals for hydrogen bonds in small water clusters — •B. Santra1, A. Michaelides1,2, and M. Scheffler1 — 1Fritz-Haber-Institut der MPG, Berlin, Germany. — 2University College London, London, UK.
Recent studies have raised concerns over the ability of DFT exchange-correlation (xc) functionals to reliably describe the structure and properties of liquid water. Hoping to shed light on this issue, we have performed systematic studies of the true ability of several DFT xc functionals to describe hydrogen bonds in small water clusters, making reference to 2nd order Møller-Plesset perturbation theory and diffusion quantum Monte Carlo[1,2]. Errors from basis set incompleteness have been minimized in both the reference data and the DFT calculations. For the total binding energies, the hybrid X3LYP and PBE0 functionals offer the best performance - with absolute errors <10 meV/H2O - and among the pure generalized gradient approximation functionals, mPWLYP and PBE1W perform best. But when the relative energies of different low energy isomers become important, problems with the xc functionals are encountered. Specifically, for the water hexamer, none of the xc functionals tested predict the correct low total energy isomer. Many-body decompositions of the total interaction energies of the clusters indicates that van der Waals forces need to be accounted for in order to correctly discriminate between different isomers with similar energies. The relevance of these results to DFT simulations of liquid water is also briefly discussed. [1] B. Santra et al. J. Chem. Phys. 127, 184104 (2007). [2] B. Santra et al., J. Chem. Phys. (in press).