Ab initio Study of Valley Line on a Total-Energy Surface for Zone-Center Distortions of Ferroelectric Perovskite Oxides BaTiO3 and PbTiO3

TL;DR

This paper introduces a new ab initio method to analyze the valley line on the energy surface for zone-center distortions in ferroelectric perovskite oxides, applied to BaTiO3 and PbTiO3, revealing different energy behaviors.

Contribution

A novel ab initio technique for determining the valley line on the total-energy surface of ferroelectric oxides, improving upon previous methods.

Findings

Total energy is a fourth-order function of atomic displacement in BaTiO3.

Total energy does not follow a fourth-order function in PbTiO3.

The method provides insights into zone-center distortions of ferroelectric materials.

Abstract

An ab initio structure optimization technique is newly developed to determine the valley line on a total-energy surface for zone-center distortions of ferroelectric perovskite oxides and is applied to barium titanate BaTiO3 and lead titanate PbTiO3. The proposed technique is an improvement over King-Smith and Vanderbilt's scheme [Phys. Rev. B 49, p.5828 (1994)] of evaluating total energy as a function of the amplitude of atomic displacements. The results of numerical calculations show that total energy can be expressed as a fourth-order function of the amplitude of atomic displacements in BaTiO3 but not in PbTiO3.