Evaluation of microscopic origins of optical responses: based on rigorous atomic space tessellating

Abstract

Clarifying the contribution of various atoms and structural units formed in nonlinear optical (NLO) crystal materials to macroscopic optical responses is crucial for NLO crystal design. In this work, the rigorous atomic space tessellating (AST) method without any empirical parameters is introduced to evaluate the correlated contributions in wavelength-dependent optical responses. The NLO crystal CsSbF₂SO₄ with a significant asymmetric electron distribution of Sb³⁺ was selected as the case study. This study indicates that there are significant differences in atomic and dipole moment contributions between the static and dynamic second-harmonic generation (SHG) susceptibilities. Using only the information obtained from the NLO-active unit analysis of static SHG susceptibilities to explain the NLO phenomenon in actual photoexcitation can even lead to qualitative errors. Among all the transitions in SHG effects, the on-site transition of Sb has the largest component, while the O–Sb off-site transition with multiple transition channels contributes the most to the macroscopic SHG susceptibilities. The relevant methods have also been extended to linear optics and used to study the anisotropy of first-order susceptibilities, which is important for achieving phase matching. Sb³⁺ contributes significantly to the linear optical anisotropy with the same sign as SO₄²⁻.