Recent Advances in ab initio time-dependent Hartree-Fock thoery and their applications to predict nonlinear optical properties of semiconductor nanoclusters

摘要

Recent advancements in ab inito time-dependent Hartree-Fock (TDHF) theory have made it a technique of choice for modeling naoscale nonliena roptial (NLO) materials from first-principles. We have used this method to study structure-NLO property relationships of GaN, GaP and GaAs clusters. The geometry of the clusters used in the study was optimized by ab initio Hartree Fock (HF) calculations with the use of even tempered Gaussian (ETG) basis set. The clusters used in this study are of the type Ga_mX_n(m=1, 3, 4, 7 and n = 1, 3, 4, 7) where X=N, P, and As. The Ga_mX_n clusters are in a charge neutral (q=0) state for m = n and in appropriately charged state for m not = n. The magnitude of the calculated (hyper) polarizabilities appears to strongly depend on the composition of the cluster. For the same composition of heteroatoms, the hyperpolarizability depends on the size as well as the geometry of the cluster. The cluster size-dependence of calculated (hyper) polarizabilities is more pronounced for the first-hyperpolarizability, beta, than for the polarizabiity, alpha. The claculated beta (-omega_sigma; omega_1, omega_2) corresponding to various second order effects shows the follwing trend beta(-2omega; omega, omega) > beta (-omega; 0, omega) > beta (0; 0, 0).