Accurate Intermolecular Potentials with Physically Grounded Electrostatics

A strategy is proposed to include the missing charge penetration energy term directly into a force field using a sum over pairwise electrostatic energies between spherical atoms as originally suggested by Spackman. This important contribution to the intermolecular potential can be further refined to reproduce the accurate electrostatic energy between monomers in a dimer by allowing for the radial contraction-expansion of atomic charge densities. The other components of a force field (exchange-repulsion and dispersion) are parametrized to reproduce the accurate data calculated by symmetry-adapted perturbation theory (SAPT). As a proof-of-concept, we have derived the force field parameters suitable for modeling intermolecular interactions between polycyclic aromatic hydrocarbons (PAH). It is shown that it is possible to have a balanced force field suitable for molecular simulations of large molecules avoiding error cancellation to a large extent.