A molecular modelling capability for predicting the purity and morphology of solids manufactured via crystallisation is important in the realisation of a 'molecule-up' or product-centred, approach for the optimisation of chemical processes. Recent work on producing the morphology of molecular solids based upon the molecular and crystal chemistry is presented. The approach is based on the atom-atom method for calculating surface attachment energies, and from these relative crystal growth rates as a function of crystallographic growth direction. The computations have been recently [2,13-15] developed to be able to treat the effects of impurity species that influence morphology. Molecular modelling procedures include an optimisation of the position and orientation of the adsorbed additive within the host lattice hence, simulating the crystal chemistry of the hetero-species within the host lattice. Case studies include naphthalene and phenanthrene in the presence of biphenyl impurity and caprolactam in the presence of synthesis impurities.