Microscopic calculation of collective excitations in He4 clusters

We compute the ground-state structure and collective-excitation energies of He4 droplets at zero temperature. The collective excitations are described by a generalized Feynman theory with inputs of exact one- and two-body densities sampled from a second-order diffusion Monte Carlo algorithm. The monopole transition density shows a pronounced shell structure not accountable by simple Jastrow-type variational trial functions.