Dynamics of ⁴He droplets

An attempt is made to advance the theoretical description of helium clusters by two aspects. First, going beyond the simple Feynman approximation for calculating excitation energies, effects due to the coupling between different excitations are included. Second, excitations with higher energy are discussed in terms of the dynamic structure function S(k,ω) and the Green's function G⁽³⁾ (k,ω) for single-impurity motion.