The First-principles Study on the Optical Anisotropy of R3 Space Group Chalcogenides AX2MQ6

摘要

In order to explain the opposite phase matchability of two types of newly discovered chalcogenides,AX2MQ6 vs AX4M5Q12 belonging to the same R3 space group,the linear and nonlinear optical properties are calculated.The calculated Electron Localization Function (ELF) show the acentricity of the bonds on the Q2-ions with sp3 hybridization is the main origin of the optical anisotropy.To quantify such an acentricity,a geometric parameter,the dihedral angle between the tetrahedral undersides and the xy-planes is defined.And the calculated birefringence depends on the above defined geometric parameter and the ion radius.This correlation reasonably explains the opposite phase matchability of two closely related chalcogenide families of AX2MQ6 and AX4M5Q12 and is shedding useful light on further exploration on phase matchable IR-NLO crystals.