PROPERTIES OF PURE AND COMPOUND CLUSTERS OF SI, GE, AND PB

The properties of monoelemental Si, Ge, and Pb clusters and those of c ompound Si-Pb and Ge-Pb clusters have been studied by using semiempiri cal methods of the modified neglect of differential overlap type. The cluster size is 10 less than or equal to N less than or equal to 90 an d in compound clusters a fraction less than or equal to 0.5 of Si and Ge atoms is replaced by Pb. The calculations support and extend the re sults of recent first-principles calculations of silicon clusters. The y indicate, in fact, that for Si, Ge, and Pb elongated and spherical s tructures are both possible, the first lying lower in binding energy a t large N. Noticeable relaxation is observed in compound clusters whos e binding energies, bond lengths, and angles are substantially altered , with respect to the monoelemental ones, by the inclusion of the meta llic element.