SIMULATION OF THE STRUCTURE OF SOME SILICON-CARBIDE CLUSTERS BY THE MNDO METHOD

Simulations of the geometric and electronic structure of C-44, C-45, S i-45, C40Si5, and C44Si clusters were performed by the MNDO method. Th e geometries of the filled clusters, calculated by the MM2 method, wer e used as initial approximations. It was found that the filled cluster s C-45 and C44Si are transformed into endohedral clusters X@C-44 (X = C or Si, respectively) after energy optimization. The highest occupied energy level of the HOMO of the filled tetrahedral cluster Si-45 of T symmetry is triply degenerate and is only occupied by four electrons. The structure of Si-45(2-) dianion of T symmetry was calculated. Two filled structures for the C40Si5 cluster were found. The coordination numbers of the central Si atom in these structures are 4 and 3, respec tively.