2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/148668We perform an unitary transformation for the symmetric phonon mode of the Holstein molecular crystal hamiltonian. We show how to compute the electronic spectral functions by exact numerical diagonalisation of an effective hamiltonian fully taking account of the symmetric phonon mode, usually discarded.3 pages, Latex file, 1 postscript figureStrongly Correlated Electronstext