Ab initio study of stoichiometric gallium phosphide clusters.

We have studied the static dipole polarizability of stoichiometric gallium phosphide clusters (Ga(n)P(n) with n=2-5) by employing various ab initio wave function based methods as well as density functional theory/time dependent density functional theory (DFT/TDDFT). The calculation of polarizability within DFT/TDDFT has been carried out by employing different exchange-correlation functionals, ranging from simple local density approximation to an asymptotically correct model potential-statistical average of orbital potential (SAOP) in order to study their influences. The values obtained by using the model potential-SAOP are lower than those obtained by local density approximation and generalized gradient approximation. A systematic analysis of our results obtained using the DFT/TDDFT with several exchange-correlation functionals shows that the values of polarizability obtained within generalized gradient approximation by using Perdew-Burke-Ernzerhof exchange with Lee-Yang-Parr correlation functional and Perdew-Burke-Ernzerhof exchange-correlation functionals are the closest to the corresponding results from Møller-Plesset perturbation theory. We have found that the value of average static dipole polarizability per atom reaches the bulk limit from the above as the size of the clusters increases.