An energy partition method based on localized molecular orbitals

A new energy partition scheme based on the use of the molecular orbitals (MO) derived from an isopycnic localization of the natural MOs of the system is presented. The method is inspired in the Interacting Quantum Atoms (IQA) methodology and leads to an exact decomposition of the total energy of the molecule into intra-atomic self-energies and inter-atomic interaction energies. The latter, in turn, can be partitioned into a Coulombic or classical electrostatic part and an exchange–correlation contribution that measures the covalency of the interaction. In principle, the scheme presented can be used with both single- and multi-determinant wavefunctions. However, in the first case, and contrary to what happens in the IQA method, as long as the numerical overlap integrals between the isopycnic MOs over the atomic domains in which the physical space is divided are accurate enough, all the energy components are computed analytically. We have performed calculations in the H2 and LiH molecules, and in several Hydrogen bonded systems, and compared the results with those previously reported using the IQA methodology.