A coarse-grained density functional theory, chemical potential equalization and electric response in molecular systems

A simple coarse grained description of the electron density changes in molecular systems due to change in external potential, which may include the effect of external electric fields in addition to the potential due to the nuclei, has been proposed in terms of the induced atom-atom charges and atomic dipoles. The density functional perturbation theory has been used for deriving the expressions for the interaction energy and the effective chemical potentials in terms of these coarse grained variables. A route to the calculation of these quantities and hence the dipole polarizability of the molecular system is provided. The proposed approach would also be useful for obtaining polarizable charge based force field for intermolecular interaction in computer simulation.