First-principles study on linear and nonlinear optical properties of ZnGeP₂

The study of the linear and nonlinear optical properties of ZnGeP₂ based on density functional theory has been carried out. In order to get a more physical picture in the infrared region, terms which are considered as the phonon effect were added to the calculated refractive dispersion curves. The phonon-corrected calculation curves show excellent agreement with experimental refractive indexes, which gives a better comprehension of the linear optical proprieties in the transparent region. The static nonlinear optical susceptibility was investigated using approaches based on the “sum over states” and the 2n+1 theorem methods. Both of the results of these two methods reasonably coincided with the experimental results.