Theoretical studies of third-order nonlinear optical response for B12N12, B24N24 and B36N36 clusters

In this paper, we have calculated the third-order nonlinear optical polarizabilities corresponding to three optical processes: third-harmonic generation (THG), electric-field-induced second-harmonic generation (EFISHG) and degenerate four-wave mixing (DFWM) for B12N12, B24N24 and B36N36 clusters. The calculations have been performed by employing ab initio time-dependent density functional theory combined with sum-over-states method (SOS//TDDFT). We obtained the similar dynamic behavior of third-order NLO polarizabilities for three BN clusters. At input photon energy below 1.25 eV, the resonance enhancements of response haven't occurred. This is due to the fact that the calculated BN clusters have the large transition energy. B24N24 cluster has the larger transition dipole moments and the third-order polarizabilities of B24N24 are much larger than those of B12N12 and B36N36. We also estimate the static third-order optical susceptibility χ(3) for BN fullerene materials from the average static third-order polarizability <γ>. The static χ(3) of B24N24 fullerene materials are 1.36×10−14 esu for three NLO processes.