To implement the parameter estimation methodology outlined in Section 2.2 an appropriate tool for calculating intermolecular energy is required. While several programs are available for the calculation of the intermolecular energy and its derivatives, no such programs support the calculation of all the additional quantities needed by our methodology. In aid of this, the code Crystal Structure Optimizer -Rigid Molecules (CSO-RM) has been developed for the calculation of the intermolecular energy and its derivatives, and for the minimisation of the lattice energy .