Energy Decomposition Analysis Method Based on the\nConstrained Active Space Unrestricted Mean-Field Method

An energy decomposition analysis\nmethod based on the constrained\nunrestricted mean-field (CUHF) theory, called GKS-EDA(CU), is presented\nfor intermolecular interactions involving radicals. This method is\nable to take into account the spin contamination in both open-shell\nsinglet states and high-spin states. By using GKS-EDA(CU), the total\ninteraction energy can be divided into the terms of electrostatic,\nexchange–repulsion, polarization, and correlation. Test examples\nillustrate that GKS-EDA(CU) not only overcomes the spin contamination\nin the analysis for radical–radical interactions but also provides\ninsights into the variation of the magnetic coupling constant.