Piezo-optic tensor of crystals from quantum-mechanical calculations

Area of Science:

• Solid-state physics and materials science.
• Computational materials science and condensed matter physics.

Background:

• The piezo-optic tensor describes how crystal optical properties change under strain.
• Accurate determination of these constants is crucial for understanding material behavior and applications.

Purpose of the Study:

• To develop an automated, ab initio computational strategy for determining the full fourth-rank piezo-optic tensor for any crystal symmetry.
• To validate the method by applying it to calcium tungstate (CaWO4) and comparing results with experimental data.

Main Methods:

• Utilizing analytical energy gradients and Coupled-Perturbed-Hartree-Fock/Kohn-Sham (CPHF/KS) approach for dielectric tensor components.
• Exploiting point and translation symmetries within periodic boundary conditions for efficient computation.
• Calculating elastic constants as strain derivatives and photo-elastic constants as strain derivatives of dielectric tensors.

Main Results:

• The method successfully determined all ten symmetry-independent piezo-optic constants for CaWO4.
• Unambiguously established the positive absolute sign of the π61 constant.
• Confirmed 6 out of 10 experimentally determined constants and provided refined values for the remaining 4.

Conclusions:

• The developed automated computational strategy is reliable for ab initio determination of piezo-optic tensors.
• The study provides accurate optical and elastic properties for CaWO4, aiding material characterization.
• This approach offers a robust tool for predicting optical responses of crystalline materials to mechanical stress.