Understanding the crystallization of ice polymorphs from first principles

Abstract: The vast and complex phase diagram of water, with at least 18 different ice polymorphs, is a rich playground for the study of crystallization. Moreover, the equilibrium picture provided by the phase diagram is enriched further by the existence of a metastable liquid-liquid critical point at deeply supercooled conditions. Molecular simulations driven by relatively simple empirical models have provided valuable insights into water and ice, but have limitations to accurately describe some processes and fail completely at capturing others. First principles simulations based on quantum-mechanical forces can be more accurate and are also able to capture subtle physical phenomena, but until recently their cost was prohibitively high. In recent years, the length and time scales accessible to first principles simulations increased dramatically through the use of machine learning algorithms, and they are now a viable alternative to simulate complex phenomena. In this talk, I will discuss recent developments on the use of first principles simulations and rare-event techniques[1] to study the crystallization of ice polymorphs. I will first present results on the calculation of ice nucleation rates and other properties connected to nucleation from first principles[2]. Afterwards, I will discuss the exotic behavior of the melting lines of several ice polymorphs in the vicinity of the liquid-liquid critical point. I will conclude the talk with some thoughts about how these techniques are revolutionizing our ability to understand and predict the crystallization of materials.

Bio: Pablo Piaggi is currently a Postdoctoral Research Associate in the Department of Chemistry at Princeton University. He received his Ph.D. in Materials Science and Engineering in 2019 from EPFL (Switzerland) working in the research group of Michele Parrinello. Since 2019 he has held a postdoctoral position at Princeton University working with Roberto Car, Pablo Debenedetti, and Athanassios Panagiotopoulos. Piaggi has received several awards for his work on the use of advanced simulation methods to study phase equilibria and predict the crystal structure of materials, including the 2021 IBM Research Award. In 2019 he was awarded a postdoctoral mobility fellowship from the Swiss National Science Foundation.