Hi AAG Group, We'll be having an open discussion with Prof. Debenedetti at the theory couches at 5:40p tonight; feel free to stop by. There's one spot left for dinner (leaving Dept at 6:20) if you're interested. See below for details of his talk tomorrow. Cheers! Nicolas 02/24/16 4:00PM MIT Building 4, Room 163 Thermodynamics and Kinetics of Deeply Supercooled Water: a Computational Perspective Pablo G. Debenedetti Department of Chemical and Biological Engineering, Princeton University Water, like any other liquid, can be cooled below the equilibrium freezing temperature and still remain in the liquid state: it is then said to be supercooled. Large quantities of supercooled water exist in clouds and play an important role in ice formation, latent heat release, and in the atmosphere’s overall radiative balance. The physical properties of supercooled water have been a source of continued interest since the early ‘70s, when sharp increases in compressibility and heat capacity upon cooling were first reported. One intriguing hypothesis that has been formulated to explain this behavior is the existence of a metastable phase transition between two different liquids at deeply supercooled conditions. The preponderance of experimental evidence is consistent with this hypothesis, although no definitive proof exists to date. State-of-the-art free energy techniques provide clear evidence of a metastable transition between two distinct liquid phases in a molecular model of water. The fact that a phase transition is metastable implies that the possibility of observing it, whether in the computer or in experiments, depends on system size and on the duration of the observation. Understanding the manner in which force field details influence the existence and observability of liquid-liquid transitions is currently a subject of intense study. Although freezing is a ubiquitous phenomenon, large gaps in understanding persist regarding the detailed microscopic mechanism and the rate of ice formation at atmospherically-relevant conditions. Using state-of-the-art computational methods designed to probe rare events, we are able to study the early stages of ice nucleation at deeply supercooled conditions. We observe a competition between cubic and hexagonal ice polymorphs. Transition states are rich in the kinetically-favored cubic ice, rather than in the thermodynamically stable hexagonal ice. These examples illustrate the power of modern computational techniques rooted in statistical mechanics, as well as the considerable challenges that still lie ahead in the quest for accurate and predictive depictions of complex phenomena.