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.
Ice formation on aerosol particles is a process of crucial importance to Earth's climate and the environmental sciences, but it is not understood at the molecular level. This is partly because the nature of active sites, local surface features where ice growth commences, is still unclear. Here we report direct electron-microscopic observations of deposition growth of aligned ice crystals on feldspar, an atmospherically important component of mineral dust. Our molecular-scale computer simulations indicate that this alignment arises from the preferential nucleation of prismatic crystal planes of ice on high-energy (100) surface planes of feldspar. The microscopic patches of (100) surface, exposed at surface defects such as steps, cracks, and cavities, are thought to be responsible for the high ice nucleation efficacy of potassium (K)-feldspar particles.
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