Electronic structure studies on silylalkanes, alkylsilanes and silysilanes

The authors report ab initio calculations on the H, C, Si cluster molecules Si₂H₆, C₂H₆, SiH₃CH ₃, Si₅H₁₂, (SiH₃)₄C, (CH₃)₄Si and C₅H₁₂. The method involved the use of pseudopotentials to replace the Si core. Total energy differences show that, at least at the SCF level of theory, Coulombic stabilisation largely compensates for loss of maximal overlap, thus rendering the C-Si bond very slightly stable against disproportionation. The orbital energy changes and charge populations imply that bonding differences can be understood very largely in terms of local interactions, so that the delocalisation properties occurring in silanes must arise from second-order interactions involving relatively low-lying excited states. The tetrasilyl methane molecule is predicted to be rather stable.