Force Field Application and Development

Molecular modelling provides the molecular specificity for performing calculations on materials where the use of quantum mechanics (QM) would be computationally prohibitive. In addition, molecular modelling accounts for all force field (FF) methods, including all-atom (AA) and coarse grain (CG) methods, where all the interactions within a system are parameterised either analytically or numerically. This chapter describes a number of the most successful FFs used for geological systems, including the types of data that can be generated. It also describes the common potential forms currently used for AA and CG models, the issues of combining potential parameters and the techniques for deriving and testing both AA and CG FFs. The chapter explains the fitting procedures, that is, optimisation of the parameters, which is helped by visualising the corresponding macroscopic phenomena associated with the functional form. It reviews some of the FF libraries available for geochemical applications.