Molecular Simulations of Crystallization from Solution
CECAM-Lugano, Lugano, Switzerland
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Nucleation and growth of a crystal phase from solution is a ubiquitous phenomenon of primary importance both in natural and industrial processes.
Biomineralization phenomena as well as the production of sophisticated synthetic drugs or expensive fine chemistry compounds are just some of the processes that crucially depend on the nucleation and growth of a crystal from a dispersed and disordered phase.
The typical faceted shape of crystals, that can be observed across a wide range of length scales, is the direct consequence of the propagation of the symmetry properties of their molecular arrangement.
Understanding crystal properties and crystallization mechanisms at the molecular scale plays therefore a primary role in the quest for broadening our current understanding of crystallization.
In fact, in spite of its importance and mutlidisciplinary character, molecular details of crystallization from solution still remain only partially understood.
The identification of nucleation mechanisms, the mechanistic description of crystal shape evolution during the growth process or the influence of foreign molecules on both nucleation and growth, represent only a fraction of the open problems in this field.
In this framework, molecular simulations play a primary role, allowing to obtain an insight into the elusive phenomena that occur at the molecular scale.
The simulation of crystallization, has always been at the center of the interests in the molecular simulation community.
A wide range of techniques and molecular modelling approaches have been used to tackle the problem: Molecular Dynamics (MD), Monte Carlo simulations (MC), and Ab-initio molecular dynamics (AIMD), all belong to the vast array of techniques used to simulate crystallization processes or to compute relevant crystal properties at the molecular scale.
Moreover, the parallel and complimentary development of computer hardware and simulation algorithms allowed in recent years to overcome the time scale limitations due to the intrinsically rare events that charactere crystallization.
On the algorithm side, enhanced sampling approaches such as Metadynamics , Wang Landau Sampling , Forward Flux  or Transition Path Sampling , are becoming increasingly popular within the community interested in the simulation of crystallization processes.
The paradigmatic example of a rare event in this field is crystal nucleation. Starting from the seminal work of Frenkel and coworkers on ideal systems [5, 6, 7], molecular simulations have been broadly used to investigate nucleation.
This has allowed a vast broadening of our understanding of relevant crystallization processes such as, i.e., ice nucleation [8, 9], or calcium carbonate non-classical nucleation from solution [10, 11] or the investigation of the early stages of mineral carbonation .
However, from the combined effort of experimentalists and theoreticians, an increasing amount of evidences have been found in the last decade suggesting that the mechanism of crystal nucleation might not always follow a single-step process as suggested by classical nucleation theory [13, 10, 14, 15].
In particular a two-step nucleation mechanism that involves semi-ordered molecular clusters as intermediates emerges as a credible picture for the description of crystal nucleation from solution.
Crystal growth is also attracting a wide and interdisciplinary interest. It is crucial for the development of a mesoscopic description of crystal growth from solution to uncover the dominant growth mechanisms at the molecular scale and to identify the key aspects of the interaction between the crystal surface and the solution.
For example the development of solvent-specific crystal morphologies , needs to be considered in the design of industrial crystallization processes.
Most drugs and fine chemicals are in fact sold as crystalline solids and in recent years chemical companies have become aware of the importance of crystal morphology and the effect that it can have on processability and, in some cases, even on the final properties of the substance .
In this area, simulations aimed at understanding at the molecular level the growth mechanisms and the interactions of crystal surfaces with the solution can provide a significant contribution. They allow in fact to highlight the influence of mechanisms occurring at the molecular scale on the development of mesoscopic structures, allowing for a multi-scale approach to the growth problem [18, 19, 20].
In this framework also the adoption of molecular strategies for the calculation of energetic interactions parameters required to inform mesoscale models of crystal growth is also gaining popularity and providing a rich insight about the development of specific crystal habits .
Crystallization phenomena are ubiquitous and possess an intrinsically multidisciplinary character.
In this workshop we aim at bringing together physicists, chemists and engineers to promote the exchange of ideas from multiple perspectives about molecular simulations of crystallization from solution.
We ultimately aim at spreading concepts and methods across the boundaries of specific communities with an emphasis on molecular-dynamics based enhanced sampling approaches.
Michele Parrinello ( Swiss Federal Institute of Technology Zurich, Lugano ) - Organiser
Matteo Salvalaglio ( University College London ) - Organiser & speaker