Ab InitioCalculation of Piezoelectric and Ferroelectric Properties of NaNO2

The full set of piezoelectric stress coefficients and the spontaneous polarization of ferroelectric Im2m sodium nitrite were calculated by first-principles quantum-mechanical methods. The Berry phase approach, implemented in the periodic LCAO computational scheme, was employed with an all-electron basis set and the Hartree-Fock Hamiltonian. Suitable deformations are applied to crystal structure, and derivatives of the Berry phases are computed numerically with respect to the strain parameters, so as to obtain the eik = (∂Pi/∂ϵk)E quantities. The piezoelectric constants obtained were e21 = −0.094, e22 = 0.168, e23 = −0.092, e34 = 0.123, and e16 = −0.127 Cm−2. A spontaneous polarization value Ps = 0.169 Cm−2 was calculated for the Hartree-Fock least-energy crystal structure.