Interaction energy analysis based on canonical Kohn-Sham molecular orbitals calculation of protein

The canonical molecular orbitals (CMO) calculation provides useful knowledge such as molecular orbitals, energy level, charge density and so on. As one of the properties obtained from the CMO calculation of protein results, the interaction energy analysis between amino acid residues and/or substrates is useful as molecular design and functional analysis. The energy decomposition analysis approaches are the well-known calculation methods for interaction energy analysis, however, the electronic structure calculation of large molecule is very expensive and hard to achieve. Therefore, we have implemented the interaction analysis method by using the energy density analysis (EDA) method. The calculation for the EDA method is as simple as the Mulliken population method but requires matrix elements for energy calculation. By adopting the grid-free method for the exchange-correlation term, we could apply the EDA method in the DFT scheme.