Density functional theory calculations insight to the effect of anion on the nonlinear optical properties of LiInX2 (X = S, Se).

Abstract

The linear and nonlinear optical susceptibilities for LiInS2 and LiInSe2 are studied by density functional theory using total energy pseudo potential plane wave method. The structure, band structure, density of states, and frequency-dependent complex dielectric function ε(ω) are calculated. The direct band gap of LiInSe2 is smaller than that of LiInS2. The birefringence Δn (0) is negative for LiInS2 and LiInSe2. The imaginary and real parts of the second-order susceptibility are evaluated. It is found that χ 333 ((2)) (ω) is the dominant component which shows the largest total Re χ ijk ((2)) (0) values. The contribution from the intra-band and inter-band to the second harmonic generation is increased when S is replaced by Se. It is found that a compound with smaller energy band gap has larger values of χ 333(0) which would lead to a possible route to further enhancement of Im χ 333(ω) by band gap engineering.