Ionized And Electron-attaches States Via EOM-CC
Ionized and electron-attached states can be treated via the following schemes
The ionized- or electron-attached states are described using an equation-of-motion (EOM) CC ansatz which is equivalent to a CC linear response-theory description (i.e., for the ionized state given by an excitation into the continuum) as well as to corresponding Fock-space CC descriptions
For all schemes, open-shell treatments using UHF or ROHF reference functions are available.
Analytic first derivatives are available for the ionized state treatment at CCSD(2), CC2, and CCSD levels; for the electron-attached states they are available only at the CCSD level, and then only when the AO-based algorithms (ABCD=AOBASIS) is not used.