2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/25523Taking the same trial wave function, the ground-state energy of Fröhlich polaron is investigated by variational method and coherent-state expansion (CSE) one, respectively. Within the accuracy to $α^{2}$(the electron-phonon coupling constant), both methods can give the same analytic expressions of polaron ground-state energy as the function of electron-phonon coupling constant. We find that the CSE method can much simplify the calculation and shows more advantages in higher order approximations.6 pages, no figureOther Condensed Mattertext