A new refinement strategy

Abstract

Abstract With the greatly enhanced computational resources now available a quite different strategy has been developed for representing the intermolecular interactions in the MC models used to fit to the observed X-ray scattering. Previously effective inter-molecular interactions were represented by a relatively small set of interatomic springs. Now it is possible to use all the atom-atom pair interactions between neighbouring molecules to compute the MC energy. Rather than allowing the spring constants, Ki, to be independent variables, their values are expressed by an empirical formula that defines the Ki as a function of the pair type and the separation distance. This involves a small number of adjustable parameters that are determined by the fitting. The method is demonstrated using the example of the paracetamol polymorphs.