Abstract
The elasto-optic effect, or photoelasticity, describes the linear change of dielectric tensor with applied strain and is a universal material property of insulators and semiconductors. Though the elasto-optic responses for solids can be computed directly from first principles (e.g., by using density functional perturbation theory) and measured experimentally, these methods do not provide sufficient insight into the governing microscopic physical principles of photoelasticity. In this work, we describe a microscopic first-principles analysis of photoelasticity in real space and apply it to investigate the elasto-optic responses of Si, diamond, NaCl, and MgO. By writing the random phase approximation (RPA) dielectric constant in the basis of maximally localized Wannier functions, we show that the strain-dependent change of dipole transitions between occupied and unoccupied Wannier functions are the main determinants of photoelasticity. By organizing the dipole transitions into spatially localized shells, we develop a ``constrained sum'' method that converges both the dielectric and photoelastic responses systematically and reveals a relatively long-ranged nature to these responses: one needs to sum up contributions of up to third neighbor shells to converge the elasto-optic coefficient with reasonable precision.
Published Version
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