I am trying to run EOM-CCSD(fT) calculations on a system containing 11 heavy atoms, albeit with def2-svp basis sets.
With EOM-CCSD, I get a value of 1.08 eV. With ADC2, SCS-ADC2 & CC2, I get around 1.02-1.10 eV. Results from double hybrid TDDFT calculations are also around this range. These are all perfectly reasonable since the experimental data is around 0.99 eV. With larger def2-TZVP basis sets, results from this WFT and TDDFT methods change only minimally.
However, with EOM-CCSD(fT), the excitation energy jumps from 1.08 eV to 2.57 eV. The fT correction to the ground state is 0.055 a.u. more than for the first singlet excited state. With EOM-CC3 using another package, I get 1.06 eV, but that calculation took almost a month, requesting for 8 states in total.
Does anyone have insights into why this could be? It just seems rather odd that the fT corrections make EOM-CCSD “worse” by about 1.50 eV.
With the perturbative triples inclusion, is it possible to converge to a different energy state? With EOM-CCSD, the first and second excited states are 1.08 and 3.54 eV, respectively.
This is my input card:
MEM_STATIC = 10000
MEM_TOTAL = 120000
SYM_IGNORE TRUE METHOD EOM-CCSD(ft)
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