Ice nucleation at negative pressures using molecular dynamics: Implications for atmospheric clouds*

Mixed-phase clouds cover large portions of the planet and are highly relevant to the global climate, impacting the stability of the Arctic Ocean ice pack amongst other important climate systems. The evolution of these clouds is controlled by the process of ice nucleation in the supercooled cloud droplets. Modeling and accurate remote observation of these clouds is limited by an incomplete understanding of the physics governing the phase transition from liquid water to ice. Molecular Dynamics (MD) simulations of ice formation can help to reveal the fundamental mechanisms behind ice formation. I will briefly discuss experiments carried out at MTU that suggest a role for pressure fluctuations in nucleation. Then I will share results of evaluating homogeneous ice nucleation rates for the ML-mW and mW water models at negative pressures. Results indicate that the density difference between water and ice exhibited by these models plays a central role in controlling the change in nucleation rate. I identify an equation that provides a reasonable approximation for lines of constant nucleation rate, which can be useful in advancing the study of ice nucleation mechanisms.