Second-order M011er-Plesset Theory

The next level of sophistication is to include inter- as well as intracorrelation effects using, as advocated by Pople , M011er-Plesset perturbation theory , a true supermolecular method subject to BSSE (cf Section V). We restrict our discussion here to the frequently applied second-order variant (MP2). 

The dispersion energy (inter-monomer correlation) in the MP2 appraoch is obtained at the uncoupled Hartree-Fock level as discussed above. At longe range the result is identical to that of the polarization approach using the M011er-Plesset partitioning. No coupling between correlation effects is 

The intra-monomer correlation affects the (intermolecular) interaction energy through matrix elements of the form ° 

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