Particle number conserving approach to correlations
  In the present work the so-called Higher Tamm-Dancoff Apporximation method is presented for the generalized case of isovector and isoscalar residual interactions treated simultaneously. The role of different particle-hole excitations and of proton-neutron pairing correlations in the ground state of the self-conjugate 64Ge nucleus is discussed. 
K. Sieja, T.L. Ha, P. Quentin, A. Baran