Finite Size Corrections for the Pairing Hamiltonian
  We study the effects of superconducting pairing in small metallic grains. We show that in the limit of large Thouless conductance one can explicitly determine the low energy spectrum of the problem as an expansion in the inverse number of electrons on the grain. The expansion is based on the formal exact solution of the Richardson model. We use this expansion to calculate finite size corrections to the ground state energy, Matveev-Larkin parameter, and excitation energies. 
Emil A. Yuzbashyan, Alexander A. Baytin and Boris L. Altshuler