New energy partitioning scheme based on the self-consistent charge and configuration method for subsystems: Application to water dimer system

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Abstract
The charge-transfer energy in water dimer is analyzed. The analysis is based on self-consistent charge and configuration method for subsystems (SCCCMS). The SCCCMS, as such, is not restricted to any computational schemes and can be applied at Hartree–Fock (HF), post-HF, and density functional levels of theory. In our approach, the interaction energy is decomposed into deformation (DEF), electrostatic (ES), polarization (P), charge transfer (CT), and exchange (EX) [exchange–correlation (XC)] contributions. The CT energy is derived from the energy surface spanned in the populational space. The intermediate results obtained during construction of this energy surface, such as chemical potentials, hardness and softness parameters, are of particular interest in the theory of chemical reactivity and, thus, these values are discussed as well. The influence of basis set and computational method is analyzed. The numerical values of the energy components obtained at the HF level of theory are compared with those of Kitaura–Morokuma (KM) and reduced variational space (RVS) analyses. It is shown that SCCCMS correctly describes the polarization process. The CT contribution is less dependent on the basis set than KM or RVS scheme and is free from the basis set superposition error (BSSE). It is demonstrated that the CT energy is of little importance for the water dimer. In addition, the amount of CT calculated in our scheme is almost identical to that obtained from the supermolecule calculations.

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