Relativistic coupled-cluster calculation of core ionization potential   using the Fock space eigenvalue independent partitioning technique
  In this paper we have applied the cluster-expansion ansatz for the wave operator \Omega which incorporates the orbital relaxation and correlation effects in an efficient manner. We have used both ordinary and normal ordered cluster operator (\Omega) to compute the ionization potential for different states of Ne, Ar, and Kr. The result in our calculation clearly shows how the relaxation and correlation effects play the role in determining the ionization potential, one of the interesting aspects in theoretical spectroscopy. 
Chiranjib Sur and Rajat K. Chaudhuri