Mass enhancement in narrow-band systems

A perturbative study of the Holstein molecular crystal model which accounts for lattice structure and dimensionality effects is presented. Anti-adiaba tic conditions peculiar to narrow-band materials and an intermediate-to-str ong electron-phonon coupling are assumed. The polaron effective mass depend s crucially in all dimensions on the intermolecular coupling strengths whic h also affect the size of the lattice deformation associated with the small -polaron formation.