Electronic structure calculations and physical properties of ABX2(A = Cu, Ag; B=Ga, In; X = S, Se, Te) ternary chalcopyrite systems

The results of the electronic band structure calculations performed on ternary chalcogenides ABX(2) (A = Cu Ag; B = Ga, In; X = S, Se, Te) using the semi-relativistic Tight Binding Linear Muffin Tin Orbital method are reported. The equilibrium lattice constants and the bulk moduli obtained from the P-V curves agree very well with the experimental values. More generalized equations connecting the cell Volumes and bulk moduli as well as bulk moduli and melting points are established. It is to be noted that since these equations hold good for all I-III-VI2 compounds they could be used further for extracting the above parameters for other compounds that crystallize in the body centered tetragonal structure. The energy gap at ambient pressure is found to be direct in all the cases and the nature of the gap crucially depends on the manner in which the d-electrons of the A atoms are treated. The pressure derivatives of the energy gaps as well as the metallisation pressures are calculated and compared with the available experimental values.