Bonding in Nb3O, Nb3S and Nb3Se: A topological analysis of the electrostatic potential

The structures of different neutral and cationic isomers of Nb3O, Nb3S and Nb3Se were optimized within the framework of Kohn-Sham density functional t heory. For Nb3O, neutral and cationic, the lowest minimum is a planar C-2v structure with an edge-bound oxygen atom. The binding energy of the oxygen to the Nb-3 cluster is 184.9 kcal/mol, 185.4 kcal/mol for the cationic syst em. For Nb3S and Nb3Se, neutral and cationic, the lowest minima are three-d imensional structures. The corresponding binding energies are 137.9, 138.1, 131.8 and 132.3 kcal/mol for Nb3S, Nb3S+, Nb3Se and Nb3Se+, respectively. In order to explain the different ground state structures of Nb3O, on the o ne hand, and Nb3S and Nb3Se, on the other, in terms of the nature of the bo nding in each of them a topological analysis of the molecular electrostatic potential was performed. The different relative stabilities of two- and th ree-dimensional structures can be explained on the basis of bond critical p oints in the molecular electrostatic potential. (C) 2001 American Institute of Physics.