(Hyper)polarizabilities of isolated GaN nanoclusters

The linear and nonlinear polarizabilities of hydrogen-terminated GamNnHx (m = n = 1, 4, 7, 17) clusters have been calculated by the ab initio time-dependent Hartree–Fock method. The calculated linear polarizability per Ga–N unit for the Ga17N17H38 cluster shows excellent agreement with the corresponding value estimated from the measured dielectric constant of bulk GaN. The calculated (hyper)polarizabilities show a strong dependence upon the size and the geometry of the cluster. For clusters containing equal numbers of Ga and N atoms but differing in geometry, the structure with a reduced symmetry has a much larger first-order NLO coefficient than that with a higher symmetry.