Multi-partitioning Mّller-Plesset perturbation theory. A state-selective formulation

A state-selective (intermediate Hamiltonian) formulation of the recently proposed multi-partitioning Mّller-Plesset perturbation theory is presented. The novel approach offers the possibility to combine the decontracted treatment of the reference space parts of wavefunctions with numerical stability in the presence of intruder states and strict separability at second order. Test applications to molecular electronic structure calculations are considered.