Abstract
In this work the structure and the electronic configuration of polymorphous compound clusters of size 20 ⩽ N ⩽ 110 formed by Si, O, H are studied by using semi-empirical methods of the type LCAO. A decrease of the HOMO-LUMO gap with the increase of the cluster size is generally observed. The effect, however, depends in a complex manner on the geometry and on the composition of the cluster.