The study of the linear and nonlinear optical properties of Zn Ge P2 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 the2 n ＋ 1 theorem methods. Both of the results of these two methods reasonably coincided with the experimental results.
The structural,electronic,mechanical properties,and frequency-dependent refractive indexes of GaSe1-xSx（x=0,0.25,and 1） are studied by using the first-principles pseudopotential method within density functional theory.The calculated results demonstrate the relationships between intralayer structure and elastic modulus in GaSe1-xSx（x=0,0.25,and 1）.Doping of ε-GaSe with S strengthens the Ga-X bonds and increases its elastic moduli of C（11） and C（66）.Born effective charge analysis provides an explanation for the modification of cleavage properties about the doping of e-GaSe with S.The calculated results of band gaps suggest that the distance between intralayer atom and substitution of S（Se）,rather than interlayer force,is a key factor influencing the electronic exciton energy of the layer semiconductor.The calculated refractive indexes indicate that the doping of ε-GaSe with S reduces its refractive index and increases its birefringence.
