Zur Kollektivtheorie von Bohm und Pines

Starting from the longitudinal electron-phonon Hamiltonian and performing two suitable canonical transformations, the Hamiltonian of separated plasmons and electrons is derived. The result obtained is in good agreement with the result found by the method of the extended Hamiltonian and the corresponding subsidiary conditions. The proposed approach may be appplied to those problems in which longitudinal phonons are of no interest.