Building polarizable force fields for ionic materials and liquids

Mathieu Salanne, University Pierre and Marie Curie, Paris, France

Many modeling problems in materials science involve finite temperature simulations with a realistic representation of the interatomic interactions. These problems often necessitate the use of large simulation cells or long run times, which puts them outside the range of direct first-principles simulation. In ionic systems, it is possible to introduce physically motivated model potentials for the interactions, in which additional degrees of freedom provide a ’cartoon’ of the response of the electronic structure of the ions to their changing coordination environments and allow the compact representation of many-body contributions to the interaction energy. These potentials may then be parameterized by fitting the predicted forces and multipoles to a large body of information generated from first-principles calculations. The resulting potentials are predictive, of first-principles accuracy, and have a high degree of transferability between different systems.

In this work, interaction potentials were developed for various ionic systems ranging from molten salts (fluorides and chlorides), oxides (mainly silicates and borates) and a room temperature ionic liquid (ethyl-methylimidazolium chloride mixtures with aluminium chlorides). These potentials were validated on a wide range of properties (spectroscopy experiments, activity coefficients, electrical conductivity and viscosity data), and they now allow the prediction of many other properties which remained unknown.