Effect of pressure on the structure, elasticity and optical properties of AgGaSe2 crystal

The AgGaSe₂ crystal has garnered widespread attention due to its excellent nonlinear properties and wide infrared transmittance. However, its relatively low bandgap value leads to a lower laser damage threshold, which affects its further applications. This paper investigates the changes in the structure, elasticity, and optical properties of the AGSe crystal under hydrostatic pressure using first-principles calculations based on density functional theory. During the pressure variation from −7 GPa to 13 GPa, the volume and the lattice constant c gradually decrease, while the density increases. The lattice constant a first decreases and then increases. As pressure gradually increases, the bandgap slowly opens, reaching a peak value of 2.373 eV at 12 GPa, which increases by 0.537 eV compared to 0 GPa. Elastic constants were further calculated, and the Born stability criterion confirmed the stable structure of the crystal at 12 GPa. Additionally, Young's modulus and Poisson's ratio were calculated at different pressures. The optical property calculations show that under a pressure of 12 GPa, the peak absorption coefficient of the crystal decreases and shifts towards lower energy regions. Pressure also leads to an increase in the crystal's transmittance between 20 eV and 40 eV.