Electronic structure and related properties of the ferroelectric crystal triglycine sulfate

The electronic band structure and related physical properties of the crystal triglycine sulfate (TGS), (NH2CH2COOH)3·H2SO4, in the ferroelectric phase P21 have been calculated using the first principles Linear Combination of Atomic Orbitals (LCAO) code CRYSTAL’06 at the B3LYP level of theory. The interactions between the quasi-separate three glycine groups and the sulfate complex have been studied by the analysis of the density of states of the crystal. The glycine 2 group was found to be the zwitterion in the optimized structure. Ten coefficients of the elastic stiffness tensor ckl, four coefficients of the tensor of the elastoelectrical effect eki, and the spontaneous polarization Ps of TGS have been calculated for the first time and have been found to agree well with experimental data. Extrema are found in the elastoelectric coefficient e22 as a function of the strain ε2, and in the spontaneous polarization Ps as a function of the unit cell volume.