Elastic, thermodynamic and electronic properties of LaF3 under pressure from first principles

The elastic, thermodynamic and electronic properties of LaF3 in tysonite structure have been investigated by density functional theory method within the frame of the local density approximation (LDA). The calculated lattice parameters of LaF3 under zero temperature and zero pressure are in good agreement with the experimental data. The calculated elastic constants also agree well with the available experimental data and other theoretical ones. The results show that the c axis of LaF3 is slight more incompressible than the a axis. It is mechanically stable up to 21 GPa. The pressure dependences of the elastic constants, Debye temperatures, Poisson's ratio, sound velocity and mechanical stability of LaF3 have also been systematically investigated. Based on the quasi-harmonic approximation model, the thermodynamic properties of LaF3 have been studied. In the pressure range studied, the stability of the phonon is confirmed and its change tendency is revealed. The electronic structure calculations show that the tysonite phase of LaF3 is a direct band gap insulator with a value of 7.74 eV.