Which atomic charges are best adapted to describe polyoxometalates?

Abstract

AbstractStudying several polyanions different atomic charges have been considered to determine which scheme can be trusted to describe their chemistry. Focussing on hexa, hepta and octa‐anions, five types of charges evaluated with Density‐functional methods have been compared and discussed: Mulliken, Quantum Theory of Atoms in Molecules (QTAIM), Hirshfeld, Voronoi Deformation Density (VDD), and the net total Voronoi (NTV) charges. It appears that the same two groups of atomic charges predict comparable values. The first group encompasses Mulliken, QTAIM and the NTV charges and the second one Hirshfeld and VDD charges. When the two groups are compared they present two different tendencies regarding the different types of oxygen atoms that can be isolated in the studied polyanions. The absolute value of the first group charges increases with the coordination number of the oxygen atom, whereas Hirshfeld and VDD charges display the opposite variation. These two different tendencies are enhanced by the number of metal atoms in the polyanion. Surprisingly, the NTV charges, which are rarely used in comparison with the VDD, show the same trend as the QTAIM charges which emphasizes the implication of the promolecule's definition in the failure of the Hirshfeld and VDD methods in this study. The Coulomb potential shows that Hirshfeld and VDD atomic charges are not adapted to reproduce the electrostatic properties of the anions which leads to the conclusion that these two partitioning approaches can't describe correctly the chemistry of polyanions and have to be considered with care when dealing with charged species. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010