First-principles calculation of the photothreshold of a $\beta$-GaS layered crystal

The photothreshold of a $\beta$-GaS layered crystal has been calculated as a function of the thickness of the crystal using the first-principles density functional method. The final thickness of the crystal has been simulated using the periodic plate method. Two adjacent crystal plates consisting of several layers are separated by a vacuum gap with a thickness of two layers, which corresponds to the size of the unit cell of the bulk crystal. It has been shown that, in the crystal with more than 10 layers in thickness, the photothreshold almost ceases to depend on the thickness of the crystal.