Structure of hydrogenated silicon clusters. Medium-sized clusters

The structures of the SinHm clusters containing 10 to 70 silicon atoms and different numbers of hydrogen atoms are calculated in the MINDO/3 approxima tion using the Monte Carlo technique. The geometry optimization of the clus ters showed the existence of several structural varieties that determine th e optimal geometry of the clusters differing in size and hydrogen content. Small clusters (n < 20) with various geometrical configurations often have a hollow structure if the number of silicon atoms in the cluster is more th an 12. For 20 less than or equal to n < 60 and the hydrogen content m less than or equal to n, hollow spheroidal geometry is most favorable. Staring f rom n approximate to 56-60, diamond structures are more favorable. The rati o c = m/n < 1, at which the spheroidal structure remains optimal, decreases with further increase in n.