MNDO (Modified Neglect of Differential Overlay) Parameters for Silicon. Revision

摘要

While MNDO calculations, using the original parameters for silicon, have given satisfactory results in many cases, recent extensive calculations, here and elsewhere, have revealed certain inadequacies. In particular, calculations with the previous parameters showed an undue preference for divalent silicon. One manifestation of this was to be seen in reactions involving SiR2 species. Reactions involving the formation of such silylenes were invariably predicted to be much too exothermic. The original MNDO version also performed badly for compounds containing multiply bonded silicon, greatly underestimating the strengths of the multiple bonds. For example, silaethylene and silacetylene were predicted to have bond orders of 1 and 2, respectively. Large errors also occurred in calculations for compounds of silicon with other heteroatoms, most notably oxygen. MNDO has been reparametrized for silicon. The results for a wide variety of silicon-containing compounds are in much better agreement with experiment. Enthalpies of reaction and activation are compared with results from recent high level ab initio calculations.