Effect of three body transformed Hamiltonian () through full connected triples on main and satellite ionization potentials computed via valence universal EIP-MRCC method

Valence universal multi-reference coupled cluster (VUMRCC) method via eigenvalue independent partitioning has been applied to estimate the effect of H ∼ 3 on ionization potentials through full connected triple excitations S 3 ( 1 , 0 ) . H ∼ 3 is constructed using CCSDT1-A model for the ground state calculation. H 3 ∼ S 3 ( 1 , 0 ) ¯ involves n vir 4 n occ 4 operations that may lead to large time consumption. Our investigation on HF, HCl, N2 and CO molecules using cc-pVDZ and cc-pVTZ basis sets indicates that the above effect varies from 0.001 eV to around 0.5 eV (∼11.5 kcal/mol), thus suggesting that inclusion of H 3 ∼ S 3 ( 1.0 ) ¯ is essential in high accuracy calculation.