Structure and stability of BN microclusters: Ab initio calculations for (BN)n (n = 2–4)

Unrestricted Hartree–Fock calcuations coupled with second-order Møller–Plesset correlation correction were performed to study the structures and energetics of microlusters. 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 prefer the triplet spin state, whereas cyclic isomers prefer the singlet spin state. Total charge density plots show a strong dominace 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 C_2n counterparts. This similarity follows the isoelectronic principle and is of importance due to recent interest in the investigations of BN fullerene analogs. © 1994 John Wiley & Sons, Inc.