  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.
