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キーワード:
configuration interaction; coupled-pair; size extensivity
要旨:
It is demonstrated that the coupled electron pair approximation (CEPA) equations are very close to the variational condition for an energy functional. Thus, fully relaxed density matrices can be obtained without solving Z vector equations for the amplitudes. It is also shown that CEPA/1 is the only one among the various CEPA approaches which can be spin-adapted in a consistent fashion.
