First-Principles Analysis of the Raman Spectra of 2D Material YbOCl

Raman spectroscopy is an indispensable technique for characterizing two-dimensional (2D) material structures and interaction information in experiments. However, systematic theoretical Raman analysis for 2D materials remains scarce. Ytterbium oxychloride (YbOCl) is a recently discovered 2D material that belongs to the MYX (M = transition metals; Y = O, S, Se, etc.; X = halogen) family. It exhibits half-metallic ferromagnetism, which makes it a promising candidate for spintronic devices in the future. Taking YbOCl as an example, we explored the key determinants in the calculation of the Raman spectrum. The assessment of potential-energy surfaces (PES) determined by different exchange-correlation functionals (xc-functionals) and van der Waals (vdW) corrections was found to be crucial for harmonic Raman simulation. Then, the anharmonic effects of this material resulting from electron-phonon and phonon-phonon interactions were analyzed by using the quasi-harmonic approximation (QHA) method and ab initio molecular dynamics (AIMD), and these results indicate that the anharmonic effect is weak in the YbOCl crystal. Finally, temperature- and strain-dependent Raman spectra confirmed that the vdW interactions in the YbOCl crystal are considerably weaker than the chemical bonding interactions; this tenuous interlayer vdW interaction was further substantiated via Raman simulations encompassing distinct layers. Such theoretical approaches to scrutinizing the Raman spectrum furnish invaluable insights into the intrinsic structural information and interactions of materials.