  We have carried out ab-initio calculation and study of structural and
electronic properties of AgAlM2 (M = S, Se, Te) chalcopyrite semiconductors
using Density Functional Theory (DFT) based self consistent Tight binding
Linear Muffin Tin orbital (TB-LMTO) method. Calculated equlibrium values of
lattice constants, anion displacement parameter (u), tetragonal distortion
({\eta} = c/2a) and bond lengths have good agreement with experimental values.
Our study suggests these semiconductors to be direct band gap semiconductors
with band gaps 1.98 eV, 1.59 eV and 1.36 eV respectively. These are in good
agreement with experimental value within the limitation of local density
approximation (LDA). Our explicit study of the effects of anion displacement
and p-d hybridization show that band gap increases by 9.8%, 8.2% and 5.1%
respectively for AgAlM2 (M = S, Se, Te) due to former effect and decreases by
51%, 47% and 42% respectively due to later effect.
