Electron Density Based Partitioning Scheme of Interaction Energies.

In this paper, a new partitioning of the complex interaction energy is proposed. This new partitioning is based on the decomposition of the one-electron and exchange-correlation densities into unperturbed and deformation densities. Thus, the proposed energy fragmentation can be applied at the SCF level and post-SCF levels as long as the corresponding density matrices have been evaluated previously. It provides the typical description of the complex interaction as a summation of electrostatic, exchange-repulsion, and polarization terms. However, the new method allows splitting up the exchange-repulsion into exchange and Pauli-repulsion energies. A full theoretical description of the method is presented, and some examples of its application to small complexes are discussed. A comparison with results obtained using perturbation methods is also carried out, showing that the first order terms obtained from symmetry adapted perturbation theories are perfectly reproduced with the new method. A clear bridge between qualitative deformation density plots and quantitative measures of the interaction energy components can be established within the framework of this new partitioning scheme, giving rise to a graphical and very intuitive interpretation of the complex formation.