The ever-growing power of theoretical calculations has made it possible to accurately predict physical properties of condensed matter systems. In this Letter, using a linear combination of atomic orbitals (LCAO)-type quantum chemistry calculation package and the coupled perturbed Kohn–Sham (CPKS) method, it is shown that the bandgaps, static refractive indices, and full matrix elements of the nonlinear optical coefficients of recently found chalcogenides, which are potential mid-IR nonlinear optical crystals, can be obtained simultaneously with unprecedented accuracy. The results can serve as the foundation for future applications of those materials with optimum conditions.