CRYSTALGROWER - A NEW APPROACH TO UNDERSTANDING AND PREDICTING CRYSTAL GROWTH

This year we published in Nature a new methodology, encompassed in the new software CrystalGrower, to understand and predict the course of crystal growth. The CrystalGrower strategy provides arguably the first completely general method for simulating the growth of three-dimensional crystallites based on a small number of parameters and the specification of the saturation state of the solution. By taking the important step of circumventing the need to understand the solution speciation, which for materials such as zeolites can be extremely complex, and combining this with the use of a unique choice of tilings to decompose the solid into growth units, this has led to one of the most significant recent advances in the field of modelling crystal growth. Unsurprisingly, the CrystalGrower project has attracted major interest from researchers around the world since the publication of the Nature paper that demonstrates its' applicability to everything from zeolites and minerals, through to organic molecular crystals. Not only is this interest coming from academic groups, but also from leading industrial research laboratories who would like to use the CrystalGrower approach.
Although the CrystalGrower method is already very powerful, there are many further developments that are needed. For example, the ability to handle competing polymorphs during growth and multiple crystals. A key challenge for the next phase is also to try to move from the approach of fitting the limited number of parameters involved to experimental data, such as information from atomic force microscopy, to determining these parameters directly from atomistic calculations. This would make CrystalGrower a truly predictive tool and would revolutionize the simulation of crystal growth.
Understanding and predicting the course of crystal growth is fundamental to the control of functionality in modern materials. By understanding crystal growth at the molecular scale we have the possibility to control crystal habit, crystal size, the elimination or incorporation of defects and the development of intergrowth structures. Despite investigations for over one hundred years it is only recently that the molecular intricacies of these processes have been revealed by scanning probe microscopies. In order to bring some order and understanding to this vast amount of new information requires new rules to be developed and tested. To date, because of the complexity and variety of different crystal systems, this has relied on developing models that are usually constrained to one system only. Such work is painstakingly slow and will not be able to achieve the wide scope of understanding in order to create a unified model across crystal types and crystal structures. We have recently described in Nature a new approach to understand and predict the growth of crystals, including the incorporation of defect structures, by simultaneous molecular-scale simulation of crystal habit and surface topology using a unified kinetic 3-D partition model. This approach, adopting bespoke computer software CrystalGrower, developed in Manchester, utilises all the known experimental data in order to pin down, with much greater accuracy than hitherto possible, the important free energies associated with the key steps in the crystallisation process. Moreover, these processes are applicable to all types of crystal systems from molecular to ionic to framework crystals etc.