  Recently, the collisionless expansion of spherical nanoplasmas has been
analyzed with a new ergodic model, clarifying the transition from
hydrodynamic-like to Coulomb-explosion regimes, and providing accurate laws for
the relevant features of the phenomenon. A complete derivation of the model is
here presented. The important issue of the self-consistent initial conditions
is addressed by analyzing the initial charging transient due to the electron
expansion, in the approximation of immobile ions. A comparison among different
kinetic models for the expansion is presented, showing that the ergodic model
provides a simplified description, which retains the essential information on
the electron distribution, in particular, the energy spectrum. Results are
presented for a wide range of initial conditions (determined from a single
dimensionless parameter), in excellent agreement with calculations from the
exact Vlasov-Poisson theory, thus providing a complete and detailed
characterization of all the stages of the expansion.
