Benchmark calculations of the Fock-space coupled cluster single, double, triple excitation method in the intermediate Hamiltonian formulation for electronic excitation energies

The newly formulated intermediate Hamiltonian Fock-space coupled cluster (FS-CC) method with full singles, doubles, and triples is applied to calculate benchmark excitation energies for the N2, C2, H2O molecules and Ne atom. The intermediate Hamiltonian formulation eliminates intruder states and divergence problems which occur via the traditional FS approach. For the 14 states available the MAE is 0.03 eV and the maximum deviation is 0.16 eV.