In the past two decades there has been great progress going beyond the non-reactive approximation in classical molecular dynamics (MD) force fields (FF) to describe chemical reactions where charge flow is an essential process. At present reactive force fields are limited in their applicability to describe important phenomena such as redox reactions, electrocatalysis and ionic liquids, for which the reference charge state changes dynamically. Here we present a new model which accounts for both polarization and charge flow on an equal footing based on an explicit treatment of electrons which are free to migrate during the course of the simulation. This is achieved by splitting the atom into a positive charged core and a negative charged shell and then tuning the interaction energy between the core and shell to match the ionization potential of a specific atom type. The basic principle of this method is that when two atoms of different types approach one another the shell of the atom with the lower electron affinity will move towards the atom with the higher electron affinity and induce polarization. We show that our model can reproduce with high accuracy the dipole moments and charge distribution of various molecules calculated with all electron ab-initio methods. In addition we present for the first time a classical reactive model which can describe the dissociation of hydrogen chloride into ionic fragments in water.

Coarse-grained electron transfer model for reactive force fields

2019 Fall National Meeting

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