24.7 Excited states using linear response
(CCSD-LR, EOM-CCSD)

Excitation energies can be computed using linear response (LR) theory (also called equation of motion (EOM) approach). Accurate results can only be expected for singly excited states. The states to be computed are specified on an EOM input card, which is a subcommand of CCSD. The following input forms are possible

EOM, state1, state2, state3, ...

Computes the given states. Each state is specified in the form number.sym, e.g., 5.3 means the fifth state in symmetry 3. Note that state 1.1 corresponds to the ground state CCSD wavefunction and is ignored if given.

EOM, $-n1.sym1$, $-n2,sym2$, ...

Computes the first $n1$ states in symmetry sym1, $n2$ in sym2 etc.

EOM, $n1.sym1$, $-n2,sym1$, ...

Computes states $n1$ through $n2$ in symmetry sym1.

The different forms can be combined, e.g.,

EOM, $-3.1$, $2.2$, $2.3$, $-5.3$

computes states 1-3 in symmetry 1, the second excited state in symmetry 2, and the second through fifth excited states in symmetry 3. Note that state 1.1 is the ground-state CCSD wavefunction.