A detailed theoretical study of the structural and elastic properties of magnesium silicide Mg2 Si under isotropic lattice deformation has been performed based on the first-principles' pseudopotential method. The results show that isotropic lattice deformation from 94% to 106% results in a linear decrease in the energy gap for the direct Г15-Г1 and indirect Г15-L1 transitions, while the indirect band gap Г15 -X1 increases within a range of 94%-104%, and then reduces over the range of 104%. Additionally, isotropic lattice deformation from 94% to 106% also causes a decrease in the elastic constants and modulus of Mg2 Si. Furthermore, Mg2 Si with lattice deformation from 94% to 106% is brittle, being most brittle at 94% lattice constant.
