  The theoretical formalism of the local density approximation (LDA) to density
functional theory (DFT) has been used to study the electronic and geometric
structures of SimCn (1<=m, n<=4;n<=m) clusters. An all electron 6-311++G**
basis set has been used and complete geometry optimizations of different
possible structures for a particular cluster have been carried out. Clusters
with equal numbers of silicon and carbon atoms are found to be particularly
stable. Based on the simultaneous criteria of highest binding energy, high band
gap, high ionization potential, and low electron affinity, we believe that
Si3c3 is a candidate for particularly stable or a so-called "magic cluster". A
complete comparison of the structures and the stabilities of the clusters, and
their dependence on the cluster size and the stochiometry have been studied in
detail. Binding energies, vibrational frequencies, HOMO-LUMO gaps, vertical
ionization potentials and vertical electron affinities of the optimized
clusters have been compared with other experimental and theoretical results
available in the literature.
