The validity of the rigid-atom model for electron-phonon coupling in the tight-binding approximation is examined within the linearized self-consistent theory. It is shown that the deformation-induced charge-density wave will generally reduce the strength of the coupling, thus reducing the Kohn anomaly in the phonon spectrum and the superconducting transition temperature computed from the rigid-atom model. The charge-density wave does not appear for certain modes; the optimal situation is that of the (nearly) half-filled band, when the rigid-atom model gives approximately correct results.

• Received 11 December 1970

DOI:https://doi.org/10.1103/PhysRevB.5.941