An alternative derivation of the reduced electron-phonon hamiltonian

Abstract

Using the concept of the rigidity of the electronic wave function in the superconducting phase the reduced electron-phonon hamiltonian is derived very simply without the Fröhlich-Nakajima-Bardeen-Pines transformations. The remainder term is furthermore obtained in a closed form and the connection with the Born-Oppenheimer approximation is discussed. © 1983.