Equation-of-motion coupled cluster method with full inclusion of connected triple excitations for electron-attached states: EA-EOM-CCSDT

摘要

We extend the full triples equation-of-motion (EOM) coupled cluster (CC) method to electron attached states. Proper factorization of the three- and four-body parts of the effective Hamiltonian makes it possible to achieve for the EA-EOM part a scaling no higher than n_(occ)~2n_(vir)~5. The method is calibrated by the evaluation of the valence vertical electron affinities for the C_2 and O_3 molecules for several basis sets up to 160 basis functions. For C_2, EA-EOM-CCSDT gives 3.24 eV at the extrapolated basis limit, while the experimental adiabatic EA is equal 3.27 +- 0.008 eV. For O_3 the agreement is approx 1.9 eV compared to an adiabatic value of 2.1 eV.