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arXiv · 2506.13209

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

Virginie de Mestral·Lorenzo Bastonero·Michele Kotiuga·Marko Mladenovic·Nicola Marzari·Mathieu Luisier
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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 $r_{51}$, the largest experimental Pockels coefficient of BTO, is recovered. We also reveal that $r_{51}$ 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.

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Virginie de Mestral, Lorenzo Bastonero, Michele Kotiuga, Marko Mladenovic, Nicola Marzari, Mathieu Luisier. 2025-06-16. Ab initio functional-independent calculations of the clamped Pockels tensor of tetragonal barium titanate. https://doi.org/10.1103/physrevb.111.184306

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