Perturbative expansion using variational phonon basis for Holstein model

Abstract

A simple variational displacement phonon basis, obtained through the modified Lang-Firsov (MLF) transformation, is proposed to study the Holstein model.This phonon basis contains only one variational parameter, but capable of describing lattice distortions at distant sites from the charge carrier. Perturbation method based on this MLF basis is employed to calculate the single-electron ground-state energy and static charge-lattice deformation correlation as a function of electron-phonon coupling. The energy obtained up to the second-order perturbation within this approach agrees well with the available numerical results for the entire range of coupling strength.