These are very light-weight EOM methods in which the EOM problem is solved in
the singles block and the effect of doubles is evaluated perturbatively. The
is evaluated by using either CCSD or MP2 amplitudes, just as in the
regular EOM calculations. The EOM-MP2-S(D) method, which is similar in level
of correlation treatment to SOS-CIS(D), is particularly fast. These methods are
implemented for IP and EE states. For valence states, the
errors for absolute ionization or excitation energies against regular EOM-CCSD
are about 0.4 eV and appear to be systematically blue-shifted; the EOM-EOM
energy gaps look better. The calculations are set as in regular EOM-EE/IP, but
using METHOD = EOM-CCSD-SD(D) or METHOD = EOM-MP2-SD(D).
State properties and EOM-EOM transition properties can be computed using these
methods (reference-EOM properties are not yet implemented). These methods are designed
for treating core-level states.
J. Chem. Phys.
(2017), 147, pp. 014107.
Note: These methods are still in the experimental stage.