We present a wavefunction intended to model the static correlation of molecular systems. This wavefunction is best understood as a generalization of the perfect pairing (PP) approximation, and it is therefore temed the imperfect pairing (IP) approximation. The energy is detemined by exploiting the connection between PP and a constrained coupled-cluster approach, and optimizing the orbitals to minimize the energy. We obtain results for some trial systems and find that, while a larger fraction of the correlation energy is recovered in IP and PP, and newer method has certain systematic limitations.
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