Many-Body Approximations in the sd-Shell Sandbox
  A new theoretical approach is presented that combines the Hartree-Fock variational scheme with the exact solution of the pairing problem in the finite orbital space. Using this formulation in the sd-space as an example, we show that the exact pairing significantly improves the results for the ground state energy 
R.A. Sen'kov, G.F. Bertsch, B.A. Brown, Y.L. Luo, and V.G. Zelevinsky