Structure and stability of B8 clusters

We investigated various isomers of B-8 clusters with ab initio (MP2) and density function theory (DFT) methods (B3LYP and B3PW91). Nineteen B-8 isomers were determined to be local minima on their potential energy hypersurfaces by the B3LYP, B3PW91, and MP2 methods. Fifteen of these structures are first reported. The most stable neutral B, cluster is the regular heptagon, with another boron atom at the center (D-7h, triplet), in agreement with results reported previously. The natural bond orbital (NBO) analysis and nucleus-independent chemical shifts (NICS) further reveal that the most stable species have delocalized pi bond and multicentered sigma bonds and therefore exhibit multiple-fold aromaticity. (C) 2004 Wiley Periodicals, Inc.