Ground state energy fluctuations in the Nuclear Shell Model
  Statistical fluctuations of the nuclear ground state energies are estimated using shell model calculations in which particles in the valence shells interact through well defined forces, and are coupled to an upper shell governed by random 2-body interactions. Induced ground-state energy fluctuations are found to be one order of magnitude smaller than those previously associated with chaotic components, in close agreement with independent perturbative estimates based on the spreading widths of excited states. 
Victor Velazquez, Jorge G. Hirsch, Alejandro Frank, Jose Barea and   Andres P. Zuker