(121f) Description of Heterogeneous Ice Nucleation on Substrates Inducing Substantial Interfacial Pre-Ordering

Ice nucleation plays a crucial role in several environmental and technological applications. It is, therefore, critical to understand its complex mechanism at a molecular level. Due to the activated nature of nucleation, however, conventional molecular dynamics (MD) simulations are often incapable of efficiently probing its kinetics and mechanism. Instead, it is necessary to augment MD with advanced sampling techniques, which often requires the identification of a suitable collective variable (CV)- or an order parameter (OP)- that quantifies the progress of nucleation. Ideally, a good OP will be highly predictive of the committor probability—the likelihood that a trajectory initiated from a specific configuration will culminate in the crystalline phase.

Building on a computational framework from our previous work [1], we extensively examine how surface properties and OP implementation details impact the performance of heterogeneous nucleation OPs [2]. In particular, we investigate how surfaces that induce considerable pre-ordering impact the performance of standard OPs. One means of achieving this is to utilize substrates that share certain structural features of the hexagonal ice lattice but differ slightly (e.g., in terms of atomic spacing). Small lattice mismatches between the crystal and substrate will substantially lower the nucleation barrier without eliminating it altogether. We demonstrate that small lattice mismatches compromise the ability of standard OPs to describe the progress of heterogeneous nucleation and discuss the refinement strategies that can be utilized to improve OP performance. These findings are key to systematic investigations of heterogeneous ice nucleation on potent ice-nucleating surfaces that inevitably induce considerable pre-ordering at the interface.

[1] Domingues, T. S., Hussain, S., & Haji-Akbari, A. (2024), Divergence among Local Structure, Dynamics, and Nucleation Outcome in Heterogeneous Nucleation of Close-Packed Crystals. The Journal of Physical Chemistry Letters, 15(5), 1279–1287. https://doi.org/10.1021/acs.jpclett.3c03561

[2] Sinaeian, K., & Haji-Akbari, A. (2025). The Impact of Hydration Shell Inclusion and Chain Exclusion in the Efficacy of Reaction Coordinates for Homogeneous and Heterogeneous Ice Nucleation. arXiv:2504.00362 [physics.chem-ph]. Available at: https://arxiv.org/abs/2504.00362. Manuscript accepted for publication in the Journal of Chemical Physics.