Electronically Excited States Via CC-LREOM-CC
Electronically excited states can be treated via the following schemes
At the CC levels, the excited-state description is achieved using linear-response theory (equivalent to equation-of-motion).
For all schemes except CCSDT-n, CC3, and CCSDT, open-shell treatments using UHF or ROHF reference functions are available
Excited states for CC methods involving higher than triple excitations are possible using the MRCC code by M. Kállay which has been interfaced to CFOUR.
Analytic first derivatives are available for the excited-state treatment at CIS, CIS(D), CCSD(2), CC2, and CCSD level for both closed- and open-shell reference functions. Excited-state gradients for CC approaches with higher than double excitations are available using the MRCC code by M. Kállay which has been interfaced to CFOUR.