  The similarity transformed equation of motion coupled cluster (STEOM-CC)
method is benchmarked against CC3 and EOM-CCSDT-3 for a large test set of
valence excited states of organic molecules studied by Schreiber et al. [M.
Schreiber, M.R. Silva-Junior, S.P. Sauer, and W. Thiel, J. Chem. Phys.
$\textbf{128}$, 134110 (2008)]. STEOM-CC is found to behave quite
satisfactorily and provides significant improvement over EOM-CCSD, CASPT2 and
NEVPT2 for singlet excited states, lowering standard deviations of these
methods by almost a factor of 2. Triplet excited states are found to be
described less accurately, however. Besides the parent version of STEOM-CC,
additional variations are considered. STEOM-D includes a perturbative
correction from doubly excited determinants. The novel STEOM-H ($\omega$)
approach presents a sophisticated technique to render the STEOM-CC transformed
Hamiltonian hermitian. In STEOM-PT, the expensive CCSD step is replaced by
many-body second-order perturbation theory (MBPT(2)), while extended STEOM
(EXT-STEOM) provides access to doubly excited states. To study orbital
invariance in STEOM, we investigate orbital rotation in the STEOM-ORB approach.
Comparison of theses variations of STEOM for the large test set provides a
comprehensive statistical basis to gauge the usefulness of these approaches.
