Upgraded formulation of the nuclear eigenvalue problem in a microscopic multiphonon basis

An equation of motion method for solving the nuclear eigenvalue problem in a basis of microscopic multiphonon states is reformulated consistently in terms of Tamm-Dancoff phonons. The potential and limits of the method are illustrated through the calculation of the nuclear response to dipole and quadrupole external fields in 16O. The calculation is performed using either a Nilsson or a Hartree-Fock basis. The role of the multiphonon states is shown to depend strongly on the choice of the basis. The effect of the truncation of the three-phonon subspace is also discussed.