Electron correlation effects on structural and cohesive properties of closo-hydroborate dianions (BnHn)(2-) (n=5-12) and B4H4

Results of ab initio and density functional calculations for the geometries and cohesive energies of the closo-hydroborate dianion series BnHn2- (n = 5-12) and the hypothetical borane B4H4 are presented. The purpose of this c ontribution is three-fold: first we provide an in-depth comparison of the p erformance of a whole range of different quantum chemical standard methods ranging from Hartree-Fock over density functional theory and second-order m any-body perturbation theory to the coupled-cluster method for the geometri es. Second, we give quantitative insight into the relative stabilities of t he various cluster compounds. Finally, we investigate approximations in ab initio calculations, making use of the locality of electron correlation in the occupied and virtual orbital spaces.