The generalized phonon density of states for Al nanoclusters was studied theoretically using molecular dynamics. By doing this anharmonic effects could be fully considered. In order to investigate the structure of the clusters we have also calculated the structure factor S(q)(Fourier transform of the pair correlation function). The calculations were done for systems consisting of 500 atoms and at several temperatures. Stable and metastable cluster states are observed : The clusters in the metastable state show a well defined peak in the structure factor S(q) which we interpret as superstructure. The appearance of the superstructure in the metastable state is accompanied by substantial change in the phonon density of states.