A Simple Electron-Density Based Force Field Model for High-Energy Interactions between Atoms and Molecules

In high-energy molecular dynamics or Monte-Carlo simulations, standard force fields that are optimised for simulations at ambient temperature are inadequate. This is largely because their repulsive part has been regarded as not very significant even well below zero interaction energy. It is therefore not obvious which force fields to resort to for simulating hot gases or plasmas. A Force Field model which uses the electronic densities of non-interacting atoms or molecules within the pair approximation is introduced. We start by deriving a naïve model that neglects any exchange and correlation effects between the electronic clouds and then correct this model by adding a term calibrated from ab initio calculations using CCSD(T)/cc-pVTZ level of theory. The resulting expression can be regarded as a simple exchange-correlation functional. We compare the results for the repulsive part of the potential energy hyper-surfaces with force fields commonly used on some dimers of small molecules.