First-principles calculations of phonons and Raman spectra in monoclinicCsSnCl3

Abstract

Density functional perturbation theory is used to calculate the phonons at the zone center for monoclinic ${\mathrm{CsSnCl}}_{3}$. We report the calculated normal mode frequencies classified according to irreducible representations for both infrared-active and Raman-active modes. We also report the dielectric constants and Born-effective charges and investigate the anisotropy of the nonanalyticities near the zone center. The first-principles calculated Raman-active phonon frequencies and simulated Raman spectra are compared with experimental results from literature. We find that aside from the first-order allowed Raman modes of ${A}_{g}$ and ${B}_{g}$ symmetries, forbidden LO Raman modes appear prominently in the measured spectra. Several of these modes are close to or coincide with allowed modes and alter their intensity, while others appear as separate otherwise unexplained peaks. With this interpretation, good agreement is obtained with experimental mode frequencies to within a few ${\mathrm{cm}}^{\ensuremath{-}1}$.