  The influence of collective phonon excitations, due to intersite atomic
interactions, on the stability of optical lattices is analyzed. These phonon
excitations are shown to essentially reduce the ability of atoms to be
localized. The states that seem to be insulating in the absence of the phonon
excitations can become delocalized when the latter are present. The
delocalization effect exists for both long-range as well as local atomic
interactions.
