Raman spectra of fine-grained materials from first principles

TL;DR

This paper presents a first-principles computational method for accurately simulating Raman spectra of polycrystalline polar materials, accounting for complex phonon-electromagnetic interactions, and validated on several ferroelectric compounds.

Contribution

It introduces an extended ab initio approach for Raman spectra of polycrystals, including electro-optic effects, improving accuracy over traditional single-crystal methods.

Findings

Enhanced agreement between simulated and experimental spectra.

Method applicable to various polar and ferroelectric materials.

Automatable and suitable for high-throughput analysis.

Abstract

Raman spectroscopy is an advantageous method for studying the local structure of materials, but the interpretation of measured spectra is complicated by the presence of oblique phonons in polycrystals of polar materials. Whilst group theory considerations and standard ab initio calculations are helpful, they are often valid only for single crystals. In this paper, we introduce a method for computing Raman spectra of polycrystalline materials from first principles. We start from the standard approach based on the (Placzek) rotation invariants of the Raman tensors and extend it to include the effect of the coupling between the lattice vibrations and the induced electric field, and the electro-optic contribution, relevant for polar materials like ferroelectrics. As exemplified by applying the method to rhombohedral BaTiO3, AlN, and LiNbO3, such an extension brings the simulated Raman spectrum to a much better correspondence with the experimental one. Additional advantages of the method are that it is general, permits automation, and thus can be used in high-throughput fashion.