Repulsion potentials, nonempirical

The overlap model for nearly nonempirical repulsion potentials. 105... 

The interaction parameters for the water molecules were taken from nonempirical configuration interaction calculations for water dimers (41) that have been shown to give good agreement between experimental radial distribution functions and simulations at low sorbate densities. The potential terms for the water-ferrierite interaction consisted of repulsion, dispersion, and electrostatic terms. The first two of these terms are the components of the 6-12 Lennard-Jones function, and the electrostatic term accounts for long-range contributions and is evaluated by an Ewald summation. The... 

In order to calculate the optimal tunneling distances with the help of Equation (7.3), we must know the parameters b and p. For unbonded C and H atoms, these parameters have been obtained empirically from molecular conformation data as well as from the structure and properties of molecular crystals[447]. However, their values, and in particular the parameter p = 0.22, have been chosen in such a way that they provide the best description for the interaction at distances close to the sum of van der Waals radii. But, as will be clear from subsequent calculations, the proton transfer occurs at considerably smaller interatomic distances which are of the order of the sum of ionic radii. At these distances, all empirical potentials adapted for the purpose of conformational analysis lead to a sharper increase in the energy of repulsion than the potentials obtained from nonempirical calculations and from experimental data on atomic col-lisions[447]. Therefore, it seems more appropriate to carry out the calculations by taking the value of p = 0.35 A, which is characteristic for ionic crystals whose nuclei are much closer to each other[448]. In this case, the parameter b was chosen in such a way that the value of U coincided with the energy of repulsion in molecular crystals for small derivations (0.4 A) from the sum of van der Waals radii. 

---