Hydration layer structure and ice nucleation ability of K-feldspar surfaces investigated using molecular dynamics and machine learning

K-feldspar mineral dust particles have been observed to nucleate ice heterogeneously at higher supercooling compared to other atmospheric minerals. There is experimental and computational evidence pointing to the importance of high energy (100) crystallographic planes, mostly exposed in surface cracks, but the exact atomistic ice nucleation mechanism remains unknown (Kiselev et al., 2017). Recent atomistic molecular dynamics simulations did not exhibit spontaneous ice nucleation on flat (100) K-feldspar microcline surfaces (Soni and Patey, 2019). This could have been caused by inaccurate force fields, insufficient sampling time, or considering too simple surfaces that do not present active sites for ice nucleation. We try to shed new light on the phenomenon by combining molecular dynamic simulations with machine learning models. To validate the force field used in our simulations, we compare the calculated hydration layer structures with recent 3D AFM experiments at the feldspar-water interface and find good agreement between the two (Dickbreder et al., 2024). Using non-equilibrium molecular dynamics, we determine the onset freezing temperature on a large sample of K-feldspar (100) surfaces with different termination and topographical features, such as step edges, defects, and strained lattices, by looking for a potential energy jump as the simulation temperature is decreased. Machine learning models are then trained on this data set to predict the onset freezing temperature based on the characteristics of the surface, and by using feature analysis we will determine which surface characteristics enable higher onset freezing temperatures (Fitzner et al., 2020).  

 

Dickbreder, T., Sabath, F., Reischl, B., Nilsson, R. V. E., Foster, A. S., Bechstein, R., and Kühnle, A.: Atomic structure and water arrangement on K-feldspar microcline (001), Nanoscale, 16, 3462-3473, 2024. 

Fitzner, M., Pedevilla, P., and Michaelides, A.: Predicting heterogeneous ice nucleation with a data-driven approach, Nat. Commun., 1-9, 2020. 

Kiselev, A., Bachmann, F., Pedevilla, P., Cox, S. J., Michaelides, A., Gerthsen, D., and Leisner, T.: Active sites in heterogeneous ice nucleation-the example of K-rich feldspars, Science, 355, 367-371, 2017. 

Soni, A. and Patey, G. N.: Simulations of water structure and the possibility of ice nucleation on selected crystal planes of K-feldspar, J. Chem. Phys., 150, 214501, 2019.