Ab initio theory of the non-resonant Raman effect in crystals at finite temperature in comparison to experiment: The examples of GaN and BaZrS3

TL;DR

This paper develops an ab initio theory for non-resonant Raman scattering in crystals at finite temperature, accurately describing experimental observations for materials like GaN and BaZrS3, including polarization and wave vector effects.

Contribution

It introduces a comprehensive ab initio framework for first-order Raman scattering that accounts for scattering geometry, polarization, and phonon wave vectors, validated against experiments on GaN and BaZrS3.

Findings

Accurately reproduces experimental Raman spectra for GaN and BaZrS3.

Highlights differences between first- and second-order Raman scattering theories.

Provides insights into phonon-related scattering processes in complex materials.

Abstract

We present an ab initio theory of the non-resonant Raman scattering process in crystals at finite temperature in direct comparison with experiments. The theory incorporates the scattering geometry and polarization dependence of the Raman process and the small but finite wave vectors of the phonons for correctly describing the scattering with longitudinal optical (LO) modes in optically anisotropic solids. We implement the theory for first-order Raman scattering and showcase the approach for wurtzite Gallium Nitride and the complex chalcogenide perovskite BaZrS3 in comparison to experiment. We subsequently discuss several common estimates for second-order Raman scattering in complex materials, and highlight similarities and differences to established theoretical approaches and simulation protocols both from phonon theory and molecular dynamics.