Lattice Anharmonicity and Optical Absorption in Polar Crystals: I. The Linear Chain

摘要: A calculation of the optical absorption spectrum an anharmonic one-dimensional lattice alternating positively and negatively charged particles different masses is carried out using two approaches: recent theory Born Huang, ordinary second-order time-dependent perturbation theory. Closed-form expressions for are obtained both low high temperatures. It found that subsidiary peaks may be expected at frequencies other than dispersion frequency ${\ensuremath{\omega}}_{d}$. At temperatures ${\ensuremath{\omega}}_{d}$ varies as ${T}^{\ensuremath{-}2}$ or ${T}^{\ensuremath{-}3}$ depending on how certain thermal averages out. Predictions based these results made regarding which features present spectra can to persist three-dimensional lattices.