Optimisation: A QM gradient calculation is performed. QM gradients and MM gradients derived from the LJ potentials are assigned to the "central molecule" while point charge gradients and MM gradients are assigned to all other cluster atoms. Two-body corrections may be added upon these gradients. Gradients are split into molecular gradients and internal gradients. Molecular gradients are used to generate a geometry change of the cell parameters. Internal gradients are combined to represent the uniform change of all translationally equivalent atoms. The optimisation step is then formed externally using the dl-find 39 optimiser. Internal gradients are provided to dl-find, the resulting step is received and applied to the "central molecule". The change in geometry is also applied to all equivalent molecules according to Equation (13).