Improved description of the potential energy surface in BaTiO3 by anharmonic phonon coupling

Abstract

Barium titanate (BT) based materials are at the forefront of materials being searched as possible candidates for the replacement of lead-based compositions in applications ranging from piezoelectrics to energy storage devices. Computational methods are very promising to increase the efficiency of materials discovery, provided that finite temperature properties can be realistically computed using, for example, molecular dynamics (MD). In this work, we present a systematic increase of the quality of MD simulations via an alternative way to calculate anharmonic contributions to the potential energy surface (PES) of barium titanate. A large number of first-principles calculations are performed, which are subsequently used to parametrize an effective Hamiltonian. To test the effects on various physical properties, MD simulations for the determination of transition temperatures, hysteresis, and permittivity of BT are shown. Furthermore, measurements were performed on BT single crystals to compare them directly with the MD simulations. It is observed that by incorporating a large number of anharmonic couplings, the description of the local minima in the PES becomes more accurate than in previous simulations. This leads to a better prediction of phase transition temperatures and shows the importance of anharmonic couplings in barium titanate. The presented approach can be directly adapted for other perovskite structures.