EOM-CCSDT study of the low-lying ionization potentials of ethylene, acetylene and formaldehyde

The equation-of-motion coupled-cluster (EOM-CCSDT) method with full triples is applied to the vertical ionization potentials (IP) of ethylene, acetylene and formaldehyde at the basis set limit. The theoretical results are accurate enough to define a consistent set of vertical ionization potentials. EOM-CCSDT improves the IP-EOM-CCSD values by up to 0.4 eV for H2CO, 0.3 eV for C2H4 and 0.2 eV for C2H2.