Charge density treatment of the molecule-charge interaction and its relation to the electrical component of hydrogen bonding: Accuracy and distance dependence

In a previous paper [J. Phys. Chem. A 109 (2005) 5608], we developed a charge density treatment of the electrical interaction between a molecule and point charges, which was applied to the electrical component of the hydrogen-bond interaction in donor-molecule/acceptor-charge model systems. This approach has two important advantages: it is very accurate by avoiding the deficiencies of multipole treatments, and it provides a complete electrostatic, polarization, and hyperpolarization description of interaction forces as well as energies. In this paper, we present a more general treatment of the theory and an extended demonstration of the physical accuracy of this approach, and we explore the geometric dependence of the parameters of this treatment (charge density, linearly and non-linearly induced charge density, and their derivatives) for a series of fluoromethane molecules interacting with a two-site FH. We find that, for variation in linear separation along the C-H⋯F-H line, these parameters are very well represented by a αr−β dependence, α and β being constants. For a large number of configurations, the relative rms between the predicted energies and atomic forces and the ab initio calculated values is ∼3-5%. This study opens the way to a more complete description of the three-dimensional characterization of these parameters.