First Principles Study Of The High Pressure Phase Transition,Electronic Structure,Optical Properties And Thermodynamics Properties Of AgAl Se₂ Crystals

The chalcopyrite material is a widely used semiconductor material with excellent thermoelectric,photoelectric and nonlinear optical properties,which can be used to make thermoelectric devices,photoelectric devices,optical devices and other important devices.The chalcopyrite material has also excellent potential applications in solar cells,optical devices,etc.The AgAlSe₂ crystal is a chalcopyrite structure under general conditions.When the material is in a high-pressure extreme environment,its structure may undergo microscopic changes.Microscopic changes in the structure may cause changes in its macroscopic properties.This paper discusses the crystal structure,lattice dynamic stability,electronic structure,thermodynamic properties and optical properties of AgAlSe₂ under high pressure based on density functional theory.The conclusions are as follows:?1?The pressure of the crystal structure of chalcopyrite AgAlSe₂ is gradually increased,and the change of the crystal structure parameters is studied.With the gradual increase of pressure,the volume and density of AgAlSe₂ crystals gradually decreased,the rate of change of bond length between Ag-Se and Al-Se,and the lattice constant a and c tended to decrease slightly with the increase of pressure.At 13.9GPa,the volume,density,bond length,lattice constant a and c suddenly changed,which shows that chalcopyrite structure AgAlSe₂ is no longer stable near 13.9GPa and has structural mutation.?2?The lattice dynamics stability of chalcopyrite AgAlSe₂ is determined by calculating the phonon scattering spectra under different pressures.The virtual frequency of the phonon scattering spectrum of Ag AlSe₂ crystal appears,indicating that the structure is unstable at 13.9 GPa.According to the analysis of the electronic structure and charge layout number under different pressures,the charge distribution at13.9 GPa changes suddenly.?3?Under different pressures,the real and imaginary parts of the dielectric function of the Ag AlSe₂ crystal perpendicular to the c-axis direction and parallel to the c-axis direction tend to blue shift and do not coincide with each other.The optical properties of different directions?dielectric function,absorption coefficient,complex refractive index?gradually increase with the increase of pressure,and the difference is more obvious,the anisotropy is more obvious with the increase of pressure.?4?The rate of change of the Debye temperature?_D of the AgAlSe₂ crystal increases slightly with pressure.When the pressure is greater than or equal to 13.9GPa,the rate of change of the Debye temperature?_D with temperature is particularly obvious.The enthalpy H,heat capacity C_V,and entropy S curves increase with pressure,their rate of change has decreased slightly...