Moller-Plesset perturbation theory second-order energy derivatives

We state without further derivation that the electronic energy corrected to second order in Moller-Plesset perturbation theory, mp2 is... 

First principles methods need less parametrisation, since the hamiltonian is built up from more fundamental principles, although simplifications and even some level of parametrisation remains necessary for practical use. For instance, in the case of DFT, that point is particularly evident in the construction of the exchange-correlation energy functional, which is not known a priori for an arbitrary molecular system. ° In the case of Hartree-Fock, the correlation effects are not considered and post-Hartree Fock adjustments are necessary to include such effects, for instance in the form of perturbative expansion terms of the type derived in the Moller-Plesset perturbation theory of second order (MP2). ... 

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