First principles study of structural stability, electronic and related properties of (NH4)2SO4

The electronic structure and related physical properties of crystalline ammonium sulfate, (NH4)2SO4, have been studied using the first principles code CRYSTAL06 at the B3LYP level of theory. The title compound has been found to possess one stable and three metastable configurations, all within the polar space group Pna21 (no. 33). Two of the metastable polymorphs are newly predicted and have not yet been observed experimentally. The different configurations show considerably varying magnitudes of the spontaneous polarization Ps. All coefficients of the elastic stiffness tensor, ckl, and elasto-electrical tensor, eki have been calculated for the first time and have been found to agree satisfactorily with experimental data, as far as available.