Constrained dipole moment density functional theory for the calculation of the charge-transfer energy in non-covalent complexes.

The original constrained dipole moment density functional theory allows one to control the magnitude of the molecular dipole moment in a variational and non-empirical way. In this work, we extend this methodology to control the three Cartesian components of the molecular dipole moment. The new theoretical development is suitable for the calculation of the charge-transfer energy contributions to the total interaction energies in non-covalent complexes. To test the reliability of the theoretical development, we form three sets of non-covalent complexes from the literature with a total of fifty-one systems. The former set of complexes includes many different types of non-covalent interactions, the second set consists of prototypical non-covalent complexes and three biologically relevant interactions between DNA base pairs, and the third set comprises halogen bonding complexes. We determined the charge-transfer energy contributions and the total interaction energies of all these complexes. The calculated charge-transfer energies are in very good agreement with the ones calculated using the fragment-based Hirshfeld methodology, which has been proven to be reliable. Nevertheless, the new procedure relies on the molecular dipole moment, which is observable, while the fragment-based Hirshfeld methodology relies on a definition of a population analysis.