Accurate dipole polarizabilities of small silicon clusters from ab initio and density functional theory calculations

We report conventional ab initio and density functional theory calculations for the static dipole polarizability for the small silicon clusters Si-3 to Si-7. Our effort relies on the design of flexible basis sets of Gaussian-type functions. The dependence of the calculated mean polarizability per atom ((alpha) over bar /n) on basis set type and level of theory is brought forth and discussed. The effect of electron correlation is found to be small for all studied clusters. The density functional theory based methods are seen to predict reliable values for ((alpha) over bar /n). By introducing and analyzing the differential mean polarizability per atom, (alpha) over bar (diff)/n=(alpha) over bar (Si-n)/n-(alpha) over bar (Si), we show that in fact ab initio and density functional theory calculations yield distinctly different pictures of the polarizability of small silicon clusters. Computational strategies are proposed for the extension of theoretical studies to larger structures. (C) 2003 American Institute of Physics.