  Using the framework of nuclear energy density functionals we examine the
conditions for single-nucleon localization and formation of cluster structures
in finite nuclei. We propose to characterize localization by the ratio of the
dispersion of single-nucleon wave functions to the average inter-nucleon
distance. This parameter generally increases with mass and describes the
gradual transition from a hybrid phase in light nuclei, characterized by the
spatial localization of individual nucleon states that leads to the formation
of cluster structures, toward the Fermi liquid phase in heavier nuclei. Values
of the localization parameter that correspond to a crystal phase cannot occur
in finite nuclei. Typical length and energy scales in nuclei allow the
formation of liquid drops, clusters, and halo structures.
