Ab initio functional-independent calculations of the clamped Pockels tensor of tetragonal barium titanate

2025/06/16 by de Mestral, Virginie, Bastonero, Lorenzo, Kotiuga, Michele +3
#FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci)

paper · doi:10.48550/arxiv.2506.13209

Abstract

We present an ab initio method to calculate the clamped Pockels tensor of ferroelectric materials from density-functional theory, the modern theory of polarization exploiting the electric-enthalpy functional, and automated first- and second-order finite-difference derivatives of the polarizations and the Hellmann-Feynman forces. Thanks to the functional-independent capabilities of our approach, we can determine the Pockels tensor of tetragonal barium titanate (BTO) beyond the local density approximation (LDA), with arbitrary exchange-correlation (XC) functionals, for example, PBEsol. The latter, together with RRKJ ultra-soft pseudo-potentials (PP) and a supercell exhibiting local titanium off-centering, enables us to stabilize the negative optical phonon modes encountered in tetragonal BTO when LDA and norm-conserving PP are combined. As a result, the correct value range of r₅₁, the largest experimental Pockels coefficient of BTO, is recovered. We also reveal that r₅₁ increases with decreasing titanium off-centering for this material. The lessons learned from the structural, dielectric, and vibrational investigations of BTO will be essential to design next-generation electro-optical modulators based on the Pockels effect.

Citations

• First-principles Hubbard parameters with automated and reproducible workflows
• First-principles Phonon Calculations with Phonopy and Phono3py
• Quantum ESPRESSO toward the exascale
• Advanced capabilities for materials modelling with Q uantum ESPRESSO
• QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Non-linear optical susceptibilities, Raman efficiencies and electrooptic tensors from first-principles density functional perturbation theory
• Ab initio phonon dispersion curves and interatomic force constants of barium titanate

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