A Robust Approach for Analyzing Vibrational Motions via Polarizability and Dipole Moment

Vibrational spectroscopy, including infrared (IR) absorption and Raman scattering, is a powerful technique for investigating the structural and chemical properties of materials.This study introduces a robust approach for analyzing vibrational modes using polarizability and dipole moment variations derived from density functional perturbation theory-based calculations.By leveraging the electrostatic potential and Mulliken charges, this method provides quantitative insight into vibrational activities, enabling the determination of IR-and Raman-active modes.In particular, our findings reveal that monolayer transition metal dichalcogenides (TMDs) exhibit Raman-inactive but IR-active behaviors in the 2 () mode.Conversely, bilayer TMDs exhibit Raman-active but IR-inactive behaviors consistent with the point group theory.This approach facilitates the analysis of vibrational modes under diverse environmental conditions, such as applied strains or defects, without requiring significant experimental effort.The simplicity and versatility of this method provide a robust framework for studying vibrational spectroscopic properties across a wide range of materials and applications.