Statistical Thermodynamics & Molecular Simulations (STMS) Seminar Series: Prof. Luis McDowell (Universitad Complutense de Madrid), Ms. Yulia Pimonova (University of Utah)

​These seminar series are aimed at providing a virtual platform for sharing scientific research in the area of statistical mechanics, molecular simulations, and computational materials science. Since early 2020, the coronavirus pandemic has disrupted many large in-person scientific gatherings, including conferences and department seminars. STMS is aimed at filling this gap, and provide a venue for dissemination of research findings and exchange of ideas in the age of COVID.  This model is being currently used by several other scientific communities, and can potentially continue even beyond the pandemic if successful. 

​Each seminar will be a 60-minute event and will comprise of a long-form (30-minute) talk by a principal investigator or a senior research scientists from academia or industry and a short-form (15-minute) presentation by a graduate student or a postdoc. The remainder of the event will be dedicated to Q&A (10 minutes for the PI, 5 minutes for the student/postdoc). Long-form speakers will be chosen by the STMS Organizing Committee, while we encourage suggestions from the community at large. Student and postdoctoral speakers can either be nominated by their advisors or can self-nominate themselves by sending a CV to the organizers.  During 2022 we expect to hold two seminar per month, and the events will take place in the last two Fridays of each month, from 10:45 AM-12:00 PM Eastern Standard Time (EST):

​This event's talks:

​Growth rates of ice in the atmosphere: From premelting films to crystal habits

​Prof. Luis McDowell (Universitad Complutense de Madrid)

​Abstract: In the atmosphere, tiny snow crystals grow as plate like hexagonal crystals, between 0 and -4 C, but have columnar shape from -4 C to -10 C and again become plate like below -10 C. The reason behind this surprising behavior has remained unknown for a long time, but most authors presently agree that it has much to do with the existence of a premelting liquid film atop the ice surface. In our studies [1,2,3,4,5] we have shown that the premelting mediated interface is best described as a compound system consisting of two surfaces which separate the premelting film from bulk ice and vapor phases [1,2]. We show how it is possible to predict premelting layer thickness as a function of pressure and temperature  from the study of premelting films along the sublimation line [2,3]. In this way, we have implemented a mesoscopic growth theory that allows us to identify a number of partially stationary regimes where ice grows continuously from the vapor phase while the premelting layer thickness remains constant [4]. The underlying physics below these quasi-equilibrium premelting films dictates the growth rate of crystals. By studying the spectrum of surface fluctuations, we are able to extract step free energies required to assess growth rate by 2-d nucleation from computer simulations. We find that the calculated step free energies exhibit an anomalous behavior that is able to explain the long standing problem of snow crystal habits in the atmosphere [5]. Our work bridges all length-scales from atomic to micron size for complex interface dominated phenomena found in ice crystals.

​References

​[1] J. Benet, P. Llombart, E. Sanz and L.G. MacDowell, Phys.Rev.Lett. 117 096101 (2016).

​[2] P. Llombart, E.G. Noya, D.N. Sibley, A.J. Archer and L.G. MacDowell, Phys.Rev.Lett. 124, 065702 (2020).

​[3] J. Luengo-Marquez, F. Izquierdo-Ruiz and L.G. MacDowell, J. Chem. Phys. 157, 044704 (2022).

​[4] D.N. Sibley, P. Llombart, E.G. Noya  A.J. Archer and L.G. MacDowell, Nature Comm., 12, 239 (2021).

​[5] P. Llombart, E.G. Noya and L.G. MacDowell, Sci. Adv., 6, eaay9322 (2020).

​Speaker Bio: Luis G. MacDowell is Professor of Chemical Physics at the Universidad Complutense de Madrid. For the last decade his research has been devoted to the statistical mechanics and computer simulation of interfaces, but he has also worked on transport properties, equations of state, electric properties, nucleation, adsorption, capillarity and crystal growth.

​He obtained his PhD in Chemistry in year 2000 under the supervision of C. Vega, where he worked on the equation of state of alkanes and the development of the group's Monte Carlo code that was employed thereafter for simulations of ice and water.  He made visiting stays with Jean-Paul Ryckaert (Bruxelles) and Kurt Binder (Mainz) and was subsequently invited by Marcus Müller and Kurt Binder to take a postdoctoral position in the Johannes-Gutenber Universitaet at Mainz, Germany (2000-2002). He obtained a Ramón y Cajal fellowship at the Complutense University in 2002, where he started a new research line on the statistical mechanics of interfaces. During that period, he obtained the first national habilitation in Chemical Physics and took a permanent position in Complutense in 2007, where he is based since then.

​His most recent work deals with the study of interfacial phenomena in ice, where he has worked on explaining the mechanisms of ice crystal growth in the atmosphere and ice friction.

​

​Can lattice energies and supramolecular synthons predict co-crystallization?

​Ms. Yulia Pimonova (University of Utah)

​Abstract: Cocrystallizing a given molecule with another is one of the major routes to adjust the physical properties of molecules in the solid state. However, most combinations of molecules either form one-component crystals or amorphous solids. To predict if molecules cocrystallize, researchers often take a thermodynamic view, inferring crystallization behavior from differences in lattice energies of computationally predicted single-component crystal structures and cocrystals. Another computationally less expensive approach is based on supramolecular synthons and posits that for a cocrystal to form, interactions between different kinds of molecules should be stronger than those between the same kind. The predictive power of these approaches has not been systematically investigated. Here, we simulate the crystallization of more than 1500 distinct pairs of chiral model molecules and calculate accurate crystal energy landscapes for all of them. Our analysis shows that thermodynamic criteria alone are unreliable in the prediction of cocrystallization. While the vast majority of cocrystals that form in our simulations are thermodynamically favorable, most systems with favorable cocrystals do not cocrystallize. Predictions based on supramolecular synthons are also error-prone: in the majority of cocrystals observed in our simulations, homo-dimers have stronger intermolecular interactions than hetero-dimers. We confirm this result by calculating the DFT energies of dimers extracted from cocrystals and single-component crystals sampled from the Cambridge Structural Database. Contrary to popular belief, our results suggest that simple thermodynamic guiding principles to predict cocrystallization are unreliable and that kinetic factors are decisive in many cases. 

​Speaker Bio: Yulia Pimonova is a Ph.D. candidate at the University of Utah's Department of Chemistry, where she conducts research on molecular crystallization processes using computational chemistry tools. Prior to pursuing her Ph.D., Yulia received her B.S. from Southern Federal University in Rostov-on-Don, Russia, where she focused on investigating non-platinum electrocatalysts for low-temperature fuel cells. In her current research, Yulia works in Michael Gruenwald's group to develop high-quality cocrystallization design principles by combining thermodynamic and kinetic effects. In addition to her research, Yulia is actively involved in outreach activities, including organizing research conferences at the department level and volunteering at sports events.