Role of polarization effects in the prediction of an orthorhombic high-pressure phase in NaBr

The pressure-induced polymorphism of NaBr has been investigated by means of a quantum-mechanical Hartree-Fock localized scheme implemented in the ab initio Perturbed Ion code. Polarization effects are included using a semiclassical model and considering constant and volume dependent ionic polarizabilities. The equilibrium cell geometry, the bulk modulus and its press-are derivative have been evaluated for the B1, B2, and B33 phases. The relative merits of several polarization models in the static description of the B33 structural parameters and phase stability diagram are analyzed. Preliminary results describing the B1 and B33 phases using a common monoclinic P2(1)/m unit cell are also reported.