Crystal Nucleation in Liquids: Open Questions and Future Challenges in Molecular Dynamics Simulations

Abstract

The nucleation of crystals in liquids is one of nature’s most ubiquitous phenomena, playing an important role in areas such as climate change and the production of drugs. As the early stages of nucleation involve exceedingly small time and length scales, atomistic computer simulations can provide unique insights into the microscopic aspects of crystallization. In this review, we take stock of the numerous molecular dynamics simulations that, in the past few decades, have unraveled crucial aspects of crystal nucleation in liquids. We put into context the theoretical framework of classical nucleation theory and the state-of-the-art computational methods by reviewing simulations of such processes as ice nucleation and the crystallization of molecules in solutions. We shall see that molecular dynamics simulations have provided key insights into diverse nucleation scenarios, ranging from colloidal particles to natural gas hydrates, and that, as a result, the general applicability of classical nucleation theory has been repeatedly called into question. We have attempted to identify the most pressing open questions in the field. We believe that, by improving (i) existing interatomic potentials and (ii) currently available enhanced sampling methods, the community can move toward accurate investigations of realistic systems of practical interest, thus bringing simulations a step closer to experiments.

Computational investigation of surface freezing in a molecular model of water

“…The development of the coarse-grained mW potential has been a major breakthrough in computational studies of water and has considerably expanded the range of accessible time and length scales (40). The popularity of mW is not only a consequence of its efficiency, but also of its remarkable success in reproducing thermodynamic and structural features of water (27).…”

Janus effect of antifreeze proteins on ice nucleation

“…Here TmAFP was chosen due to its well-established structure and its high homology to MpdAFP (17,19). We note that the direct simulation of ice nucleation is still an intimidating challenge due to the extremely large computational costs (8,36,37). We therefore use the preexisting ice that grows and passes through the AFP, which can give the molecular-level information of interplay between ice and the AFP.…”

Crystal nucleation as the ordering of multiple order parameters

“…The main theoretical tool for the study of crystallization in simple model systems are density functional theory (DFT) [92,93] and molecular simulations [2,94,95]. Two-step crystallization pathways have been suggested to occur also outside the region of stability of the dense fluid phase.…”

“…A natural extension of the ideas presented in the previous section is their application to polymorph selection, which has attracted a lot of investigations [1,2,44,103,111,[141][142][143][144][145][146].…”