  We report the structural and electronic properties of chalcopyrite
semiconductors CuInSe2, CuIn2 Se4 and Cu0.5Li0.5InSe2. Our calculation is based
on Density functional Theory within tight binding linear muffin-tin orbital
(TB-LMTO) method. The calculated lattice constants, anion displacement (u),
tetragonal distortion ({\eta} = c/2a) and bond lengths agree well with
experimental values. Our result shows these compounds are direct band gap
semiconductors. Our calculated band gaps, 0.79eV and 1.08 eV of CuInSe2 and
Cu0.5Li0.5InSe2 respectively agree well with the experimental values within the
limitation of LDA. The band gap of CuIn2Se4 is found to be 1.50 eV. The band
gap reduces by 59.57%, 23.61% and 48.82% due to p-d hybridization and reduces
by 16.85%, 9.10% and 0.92% due to structural distortion for CuInSe2, CuIn2Se4
and Cu0.5Li0.5InSe2 respectively. We also discuss the effect of bond nature on
electronic properties of all three compounds.
