3.2 Optimization of Geometry:
The modified geometrical parameters for pure SrTiO3, a = b = c = 3.944 Å, were achieved after the creativity of 2×2×1 supercell and directly related with theoretical literature data [13]. Our estimated value is virtually identical to the previously published results, demonstrating the truthfulness of calculations of first-principles. The same method adopted to dope SrTiO3with Ag atoms. The parameters of lattice were changed almost 0.0074 Å for SrTiO3 and its Ag doped sample. In comparison to our calculated lattice parameters, As shown in Table 1 that the lattice parameters of SrTiO3 structure substantially overcalculated (a, b and c=3.937 Å) due to Ag doping. Ag doping in SrTiO3 also causes a decrease in the volume of the supercell. This is Ag has ionic radius of 0.128 nm which is larger than that of Sr which is 0.113 nm.