Ab initio finite field (hyper)polarizability computations on stoichiometric gallium arsenide clusters Ga_nAs_n (n=2-9)

摘要

We report reliable ab initio finite field (hyper)polarizability values at Hartree-Fock and second order M0ller-Plesset perturbation theory (MP2) levels of theory for different geometrical configurations of small gallium arsenide clusters Ga_nAs_n with n = 2-5.We relied on all-electron basis sets and pseudopotentials suitable for (hyper)polarizability calculations.In each case,we used structures that have been established in the literature after we optimized their geometries at B3LYP/cc-pVTZ-PP level of theory.Our results suggest that the first order hyperpolarizability (beta) is much more sensitive to the special geometric features than the second order hyperpolarizability (gamma).For the most stable configurations up to ten atoms the second order hyperpolarizability at MP2 level of theory varies between 15 x 10~4 and 32 x 10~4 e~4 a_0~4E_h~(-3).In addition,we examined the polarizability per atom evolution versus the cluster size for Ga_nAs_n with n = 2-9.Our work extends earlier theoretical studies which were limited to eight atoms and exposes that the polarizability/atom of the most stable stoichiometric configurations up to Ga9As9 continues the monotonic downward trend with increasing size.Lastly,from the methodological point of view,our analysis shows that apart from polarizabilities,augmented pseudopotentials yield reliable first and second hyperpolarizability values as well.