Surface and size effects for impurities in Si clusters

Silicon clusters saturated with hydrogen atoms are used to calculate charge distributions and various properties of interstitial hydrogen as a function of the host-saturator bond length. The clusters range in size from Si2H6 to Si44H42. Most of the calculations are done at the approximate ab initio level, using the method of partial retention of diatomic differential overlap. The results are complemented with ab initio Hartree-Fock calculations. It is shown that the surface dependence is minimal when the host-saturator bond length is set to minimize the total energy of the clusters. This result is consistent with the one obtained in the case of diamond clusters. A set of rules for calculating properties of impurities in semiconductor clusters is proposed.