Electronic Structure and Optical Properties of the Novel Nonlinear LiAsSe2 Crystal

We used density functional theory based on the pseudo-potential plane wave basis set to investigate the electronic structure of the beta-LiAsSe2 crystal with a non-centrosymmetric structure and the optical properties. Our results indicate that for the linear optical properties the birefringence of LiAsSe2 is very large (>0.5) in the infrared region. The adsorption ability and photoelectric conversion efficiency of long wavelength sunlight for LiAsSe2 were found to be superior to those of CuInSe2. Regarding the nonlinear optical (NLO) characteristics, LiAsSe2 showed a very large NLO second harmonic generation (SHG) response in the infrared region and the SHG coefficient (d(33)) of LiAsSe2 is about 836.5 pm.V-1. However, poor transmission of light in the infrared region is predicted for LiAsSe2 compared to AgGaSe2. By an analysis of the band structure, the SHG response of the system could be attributed to transitions from valence bands that were mixed with contributions from Li to the unoccupied bands near the bottom of the conduction bands.