STRUCTURE AND STABILITY OF BN MICROCLUSTERS - AB-INITIO CALCULATIONS FOR (BN)(N) (N=2-4)

Unrestricted Hartree-Fock calculations coupled with second-order Moller-Plesset correlation correction were performed to study the structures and energetics of microclusters. For (BN)2, linear and rhombus forms are almost isoenergetic, whereas cyclic forms are preferable for (BN)3 and (BN)4 clusters. As a general trend, linear isomers perfer the triplet spin state, whereas cyclic isomers prefer the singlet spin state. Total charge density plots show a strong dominance of the B-N bond, indicating that the extent of its polar character becomes stronger with the increase in the cluster size. The loss of a BN monomer is shown to be the most likely fragmentation channel for both neutral and single-ionized clusters. We find that neutral (BN)n clusters have the same structural configurations as those of their corresponding C2n counterparts. This similarity follows the isoelectronic principle and is of importance due to recent interest in the investigations of BN fullerene analogs. (C) 1994 John Wiley & Sons, Inc.