Is it possible to CAP/EOM-EA-CCSD on an excited state of a molecule? eg one electron promoted from pi to pi* orbital.
In principle yes, but you need to think carefully whether it will produce a balanced description. If you attach to pi-pi* state, then the resulting configuration of the anion is (pi)^2(pi*)^1. It looks to me that you would be better off computing it by attaching to the (pi)^2 reference state. If you are interested in computing (pi)^1(pi*)2, then a better way would be do EOM-EE from (pi)^2(pi*)^1 reference.
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