Quantum interpretation of classical LiF simulations

Abstract

Recent studies have shown that classical LiF simulations can reproduce low-temperature experimental spectra when performed at a simulation temperature $T^*$ higher than the physical temperature $T$. We show that the characteristic scale of this rescaling follows naturally from quantum vibrational statistics. An effective temperature $T_{\rm eff}(T)$ is obtained by matching classical and quantum harmonic energies and is evaluated using an analytic acoustic-optical model and a first-principles LiF vibrational density of states $D(\varepsilon)$. The resulting temperature reproduces the low-temperature scale of the reported spectral temperature and approaches the physical temperature in the classical regime. Our results identify zero-point motion and Planck-Bose-Einstein statistics as the origin of the reported temperature scale.