Towards modeling laser-induced homogeneous ice nucleation from first principles Margarita Shepelenko, Leeor Kronik, Jan M. L. Martin, Leslie Leiserowitz Weizmann Institute of Science, Israel The phenomenon of ice nucleation from supercooled water, which has far-reaching ramifications for the living and nonliving world, generally occurs at a heterogeneous interface. Homogeneous ice nucleation, meaning far from pre-existing interfaces, is a challenge to induce and explore. Here we focus on laser-induced homogeneous ice nucleation reported by Nevo et al in 2020, (1) which we aim to understand from first principles. Our basic hypothesis is that the ice nuclei are formed without the help of the laser beam, but these ice nuclei are metastable. Interaction with the laser beam stabilizes the formation and growth of the nuclei. We started our computational study from ice XI, a proton-ordered orthorhombic polymorph of ice which has a triple point with hexagonal ice and gaseous water at (72 K, 0 Pa) and is stable below this temperature. (2) Ice XI is of interest for us owing the similarities between its crystal structure and that of hexagonal ice I h . By virtue of orthorhombic-to-hexagonal cell transformation applied to of ice XI crystal structure, we obtained a proton-ordered ice structure in a hexagonal-ice-like cell and were able to compare the lattice energies and other parameters of interest of ‘proton-ordered’ and disordered hexagonal ice. In order to simulate a hexagonal ice ( I h ) nucleus lying in liquid water, we made use of a model composed of 96 water-molecules (3-4) to generate a pseudo proton-disordered crystal of ice, surrounded by a water shell. This is work in progress; next, we intend to study the effect of linear and circular polarized light on the ice nucleation process. References 1. Nevo, etal., Evidence for laser-induced homogeneous oriented ice nucleation revealed via pulsed x-ray diffraction. Journal of Chemical Physics 153 , 024504 (2020). 2. A Leadbetter, etal., The equilibrium low-temperature structure of ice. Journal of Chemical Physics 82 , 424–428 (1985). 3. E Cota, WG Hoover, Computer simulation of hexagonal ice. Journal of Chemical Physics 67 , 3839–3840 (1977). 4. J Hayward, J Reimers, Unit cells for the simulation of hexagonal ice. Journal of Chemical Physics 106 , 1518–1529 (1997).
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