An exact microscopic multiphonon approach to collective modes in nuclei

We generate a microscopic multiphonon basis by constructing and solving iteratively a set of equations of motion starting from the particle-hole vacuum up to a subspace spanned by states with an arbitrary number of Tamm-Dancoff phonons. In such a basis, the Hamiltonian takes a simple form and can be brought easily to diagonal form. We show how the method can be implemented to study the anharmonic features of few giant resonances in 16O