Intermediate Hamiltonian Fock-space coupled cluster method in the one-hole one-particle sector: Excitation energies of xenon and radon

The intermediate Hamiltonian Fock-space coupled cluster method developed recently is applied to excitations in the one-hole one-particle sector, taking xenon and radon atoms as test cases. Virtual orbitals are modified to yield better approximations to orbitals occupied in excited states. The usual Fock-space coupled cluster scheme diverges for these systems, but the intermediate Hamiltonian approach converges for large P spaces and yields excitation energies in very good agreement with experiment. The average error in the calculated values for the lowest excitation energies (about 20 for each atom) is 0.6%. Predictions are made for the unobserved 8s Rydberg states of Rn.