抄録
Ferroelectricity in sodium nitrite NaNO2 has been studied from first principles. The spontaneous polarization calculated with Berry-phase theory is 0.116 C/m2, being in excellent agreement with experimental values, 0.117 C/m2 and 0.119 C/m2. In order to discuss the phase transitions, we have estimated coupling parameters J1 and J2 in the axial next-nearest-neighbor Ising model from total-energy and force calculations. As results, J1 and J2 are quite sensitive to relative displacement of NO2 molecules. The transition temperature and a role of molecular displacement in the phase transitions are discussed in detail.
