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Shell Model of BaTiO3 Derived from Ab-initio Total Energy Calculations

A shell model for ferroelectric perovskites fitted to results of first-principles density functional theory (DFT) calculations is strongly affected by approximations made in the exchange-correlation functional within DFT, and in general not as accurate as a shell model derived from experimental data. We have developed an isotropic shell model for BaTiO3 based on the PBEsol exchange-correlation functional, which was specifically designed for crystal properties of solids. Our shell model for BaTiO3 agrees with groundstate DFT properties and the experimental lattice constants at finite temperatures. The sequence of phases of BaTiO3 (rhombohedral, orthorhombic, tetragonal, cubic) is correctly reproduced but the temperature scale of the phase transitions is compressed. The temperature scale can be improved by scaling of the ab-initio energy surface.