General second‐order MCSCF theory for large CI expansions

Second‐order MCSCF theory is presented in a fashion which is capable of treating large CI expansions. This formalism is then extended to encompass a state‐average MCSCF procedure. Sample calculations on Mo2 and the ethyl radical, which involve 1698 and 2302 CSFs, respectively, are presented and a number of approximate schemes discussed.

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