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HeteroIce Report Summary

Project ID: 616121
Funded under: FP7-IDEAS-ERC
Country: United Kingdom

Mid-Term Report Summary - HETEROICE (Towards a molecular-level understanding of heterogeneous ice nucleation)

Ice formation is ubiquitous, affecting global issues like climate change and processes happening at the nanoscale, like intracellular freezing. Surprisingly, it is rather difficult to freeze pure water into ice. In fact, the formation of ice in nature happens almost exclusively heterogeneously, thanks to the presence of foreign substances such atmospheric mineral dust, which plays a role of great importance when it comes to ice formation in clouds.

One might think that, since the formation of ice is one of those most basic of everyday processes, surely it must have been studied to death and surely we must understand everything there is to know about it. Certainly it has been widely studied but to say that we fully understand the freezing of water could not be further from the truth. In fact, whilst a large body of excellent experimental work on ice formation exists, it has not yet been possible to simultaneously obtain the temporal and spatial resolution that would shed light on the molecular-level details of nucleation, that is the process responsible for the formation of ice at the molecular level.

The main objective of this project is simple and yet very ambitious: to use computer simulations to further our microscopic understanding of the heterogeneous formation of ice. To this end we have tackled the problem through two different approaches. At one end we have taken into account heterogeneous ice nucleation on simple model surfaces, trying to identify general trends and concepts while developing and validating novel computational techniques. In this respect, we have devised, implemented and applied novel computational approaches (based on modifications of Forward Flux Sampling and Seeded Molecular Dynamics) which enabled efficient and reliable simulations of ice nucleation on arbitrary surfaces, providing information about the thermodynamics and the kinetics of ice formation as well as the molecular-level nucleation mechanism [J. Phys. Chem. Lett. 7, 2350 (2016)]. Then, we have performed systematic studies of ice nucleation on idealized crystalline surfaces: we have found several trends that will guide future investigations dealing with more realistic interfaces, and we have understood the spectacular sensitivity of the kinetics of ice formation to the complex interplay between the hydrophilicity of the surface and its morphology [J. Chem. Phys. 142, 184704 (2015), J. Chem. Phys. 142, 184705 (2015), and J. Am. Chem. Soc. 137, 13658 (2015)].

The second approach focuses instead on more realistic models, in the attempt to bridge the gap between simulations and experiments dealing with the formation of ice on minerals, which are of paramount importance in atmospheric science; this is an ambitious goal that requires to take into account the complexity of the water-mineral interfaces as well as the reliability of the force fields used to model the systems of interest. As of now, we have substantially improved the efficiency of the Quantum Monte Carlo method [Phys. Rev. B 93, 241118(R) (2016)], one of the most accurate computational tools we have to benchmark e.g. the water-surface interaction strength. This allowed us to obtain the first theoretical benchmark for water adsorption on clay surfaces [J. Phys. Chem. C 120, 26402 (2016)]. In addition, we have used our novel QMC implementation to address ice formation within low dimensional carbonaceous structures [Phys. Rev. Lett. 116, 025501 (2016) and a Rapid Communications accepted at Phys. Rev. B], aiding the selection of the most appropriate exchange-correlation functional to deal with water and ice at interfaces. Concerning ice formation on minerals, we have elucidated the molecular details of ice formation on feldspar by means of a combination of computer simulations and experimental insights [J. Phys. Chem. C 120, 6704 (2016)]. We have also characterized ice nucleation on kaolinite by means of FFS and SMD simulations [J. Phys. Chem. Lett. 7, 2350 (2016)]. This is the very first example of a direct calculation of the heterogeneous ice nucleation rate for an atomistic water-clay model.

Overall our findings so far represent important steps within the community toward a reliable description of realistic heterogeneous ice nucleation scenarios, much closer to the experimental reality than has been achieved previously.


Giles Machell, (European Contract Manager)
Tel.: +44 20 3108 3020
Fax: +44 20 7813 2849
Record Number: 193270 / Last updated on: 2017-01-17
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