Pressure dependence of electronic and optical properties of Zinc-blende GaN, BN and their B0.25Ga0.75N alloy

First principles calculations are used to investigate the effect of hydrostatic pressure on the electronic and optical properties of zinc blende GaN, BN compounds and their B0.25Ga0.75N alloy. We have applied the augmented plane-wave method with the local density approximation to the density functional theory. The refractive index and its variation with hydrostatic pressure are well described. Index of refraction and its pressure derivative and both imaginary and real parts of the dielectric function are identified in the photon energy range up to 40 eV. Resulting pressure coefficients of the main gap and of the refractive index are found in good agreement with experimental data.