LAUSR

Abstract First-principles studies of the geometric structures, electronic structures and optical properties of non-centrosymmetrical (NCS) KAg 2 SbS 4 , K 2 AgSbS 4 and K 2 Ag 3 Sb 3 S 7 and centrosymmetrical (CS) KAg 2 SbS 3 and K 3 Ag 9 Sb 4 S 12 have been performed by means of density functional theory. It is indicated that although they have similarity in their anionic groups and, the electronic structures, prominent features of the optical anisotropy or second-order nonlinear optical (NLO) susceptibilities are apparently different. The calculated birefringences are 0.0537, 0.0343, 0.1324, 0.2217 and 0.0604 which are attributed to the different anionic groups [SbS 3 ] and triangles [AgS 3 ]. Also, the calculated NLO responses are about 0.5×, 1.0× and 2.0× times than that commercial AgGaS 2 (AGS, d 36 =11 pm/V) for K 2 AgSbS 4 , KAg 2 SbS 4 and K 2 Ag 3 Sb 3 S 7 , respectively. In comparison with the absolute magnitude of second harmonic generation (SHG) coefficients, the order K 2 Ag 3 Sb 3 S 7 >KAg 2 SbS 4 >K 2 AgSbS 4 is clearly established in the SHG response. Further analysis based on the real-space atom-cutting method reveals that the main sources of the SHG properties of these compounds are from the Sb-S group, especially K 2 Ag 3 Sb 3 S 7 is mainly attributed to the lone pair stereochemical activity of Sb (III)-S group.