Theoretical models for the electronic structures of hydrogenated amorphous silicon. II. Three-center bonds

Self-consistent-field $X\alpha$ scattered-wave molecular-orbital calculations have been carried out for several configurations of hydrogenated silicon clusters in order to determine the contribution of three-center bonding to the electronic structure of hydrogenated amorphous silicon. Three-center bonding of dissociated molecular hydrogen is shown to stabilize Si—Si bonds over a wide range of Si-Si distances. It can be concluded that hydrogenation can, in principle, saturate all strained as well as dangling bonds in $a$-Si. The results further indicate that a single hydrogen three-center bond is unlikely in $a$-Si:H alloys.