Communication: Explicitly correlated four-component relativistic second-order Moller-Plesset perturbation theory

We propose explicitly correlated Ansatz for four-component relativistic methods within the framework of the no-pair approximation. Kinetically balanced geminal basis is derived to satisfy the cusp conditions in the non-relativistic limit based on the Leacutevy-Leblend-like equation. Relativistic variants of strong-orthogonality projection operator (Ansaumltze 2 alpha and 2 beta) suitable for practical calculations are introduced by exploiting the orthogonal complement of the large-component basis. A pilot implementation is performed for the second order Moller-Plesset perturbation theory. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757415]