2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/81761We consider a finite Fermi-system where the residual interactions create a soft mode of the excitation spectrum. Because of the large vibrational amplitude, the standard random phase approximation does not work in this situation. We develop a regular method for constructing the anharmonic potential and illustrate the application of the formalism by a simple model.11 pages, 2 figuresNuclear Theorytext