Published April 11, 2025 | Version v1
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Ab initio functional-independent calculations of the clamped Pockels tensor of tetragonal barium titanate

  • 1. Integrated Systems Laboratory, ETH Zurich, Zurich, Switzerland
  • 2. U Bremen Excellence Chair, Bremen Center for Computational Materials Science, MAPEX Center for Materials and Processes, University of Bremen, D-28359 Bremen, Germany
  • 3. Theory and Simulation of Materials (THEOS), and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
  • 4. Materials Design SARL, Montrouge, France
  • 5. Laboratory for Materials Simulations, Paul Scherrer Institut, 5232, Villigen PSI

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Description

We present an ab initio method to calculate the clamped Pockels tensor of ferroelectric materials from density-functional theory (DFT), 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.

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References

Journal reference (Paper in which the method is described and the data is discussed)
V. de Mestral, L. Bastonero, M. Kotiuga, M. Mladenovic, N. Marzari, M. Luisier, Phys. Rev. B (under review)