A Theoretical Study on the Pressure Dependence of the Band Gap in ${\rm A^{I}B^{III}C^{VI}_2}$ Compounds

The self-consistent scalar relativistic band structure for AgGaX 2 (X = S, Se, Te) performed in chalcopyrite structure using the TBLMTO method at various pressures are reported here. Empty spheres were introduced in the calculations as the chalcopyrite structure is loosely packed. From the total energy calculations, the equilibrium lattice constant and the bulk modulus at zero pressure were calculated and these values agree well with the reported experimental values. All these compounds are found to have direct energy gap at ambient pressure with the gap widening with increased pressures which are in agreement with the experimental results. The deformation potential, dE g /dP for the compounds are also reported here. The metallisation volumes are calculated and the possibility of observing superconductivity in these compounds is discussed.