Decomposition of Møller-Plesset Energies within the Quantum Theory of Atoms-in-Molecules.

We discuss two main approaches to decompose the Møller-Plesset perturbation theory molecular energies into atomic contributions within the interacting quantum atoms (IQA) formalism, as implemented in the programs Morphy and AIMAll. For this purpose, the so-called intraatomic energies (also known as self-energies) of a representative set of 55 small molecules are compared with each other. The origin of the possible discrepancies between both approaches is analyzed, and linear models linking the two approaches are proposed for each atom type.