Structural strategy for advancing nonlinear optical effects in 1D-[MX2]∞ chains: internal distortion and atomic types

Abstract

This work aimed to alleviate the limitations of existing mid-infrared nonlinear-optics (MIR-NLO) crystals by conducting theoretical research on 1D-[MX₂]_∞ (1D = one-dimensional; M = metallic element; X = anionic element) structures in relation to NLO. An analysis was conducted on the electronic structure and optical properties of six selenides (BaZnGeSe₄, K_xBa_1−x/2Ga₂Se₄, K_xBa_1−x/2Ga_yIn_2−ySe₄, K_xBa_1−x/2In₂Se₄, BaZnSiSe₄, SrZnSiSe₄) and three arsenides (Cs₂SnAs₂, Rb₂SnAs₂, K₂SnAs₂) using first principles. Afterwards, the inherent characteristics of these 1D-[MX₂]_∞ chains were further examined. The calculation results suggest that the presence of internal distortion (non-centrosymmetric) and high electronegativity in M elements can greatly enhance the NLO capability of 1D-[MX₂]_∞ structures. Furthermore, the first-ever prediction of K₂SnAs₂'s NLO ability has been made. Ultimately, the establishment of a theoretical structure (K₂BaSn₂As₄) provides guidance for the subsequent creation of high-performance MIR-NLO crystals.