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Ionized And Electron-attaches States Via EOM-CC

Ionized and electron-attached states can be treated via the following schemes

• CCSD(2) (MP2 for the reference state) (not part of public release for EOMEA)
• CC2 (CC2 for the reference state)
• CCSD (CCSD for the reference state)

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.