Perturbation theory many-body, localized, correlation level

At the correlated level the many-body perturbation theory is applied, the localized version of which (LMBPT) has already proven to be useful in the study of molecular electronic structure. The LMBPT is a double perturbation theory, and the perturbational correction are calculated as ... 

Lauderdale et al. have used MBPT (many-body perturbation theory) and ab initio SCF methods to show, unambiguously, that although the Ng benzene analogue is a local minimum at the SCF level, at the correlated level it is a second-order saddle point on the N5 surface <92JPC1173>. 

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