PARAMETERS AND VALIDITY OF FORCE-FIELD MODELS OF SILICON USING AB INITIO CALCULATIONS ON SMALL CLUSTERS.

Ab initio quantum mechanical calculations were performed on small silicon clusters to obtain their elastic constants. The elastic force constants of the clusters were then used to calculate the parameters of several force-field models, relating the elastic strain energy to atomic positions. These force-field models were, in turn, used to calculate the phonon band structure of bulk silicon. By comparing the ab initio phonon band structures with experimental results, we have obtained useful information regarding the validity of these force-field models, as well as their appropriate sets of parameters.