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

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 de-vices. 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 anhar-monic 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 ef-fects 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.

Automated summary

By calculating the anharmonic contributions to the potential energy surface, the quality of molecular dynamics simulations of barium titanate can be improved, leading to more accurate predictions of physical properties such as phase transition temperatures. This approach can also be applied to other perovskite structures.