The results of the electronic band structure calculations performed on ternary chalcogenides ABX2 (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.

Band structure calculations of ABC 2 (A ¼ Zn, B ¼ Si, Ge, Sn, and C ¼ P, As) ternary pnictides performed using the semi-relativistic 'tight binding linear muffin tin orbital' (TB-LMTO) method within local density approximation under ambient and high pressures are reported here. 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 atom A are treated. The equilibrium lattice constants, the bulk modulus, its first derivative and the metallisation volume obtained from the total energy calculations are also reported. More generalized equations connecting cell volume (V 0 ) and microhardness (H) as well as V 0 and melting point (q m ) for pnictides are established, by use of which the values of H and q m for some pnictides are predicted for the first time in cases where experimental values are not known.

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