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Theoretical and Computational Studies of Condensed-Phase Phenomena: The Origin of Biological Homochirality, and the Liquid-Liquid Phase Transition in

Speaker: Francesco Ricci
Series: Final Public Oral Examinations
Location: Lapidus Lounge (E-Quad A210)
Date/Time: Wednesday, February 17, 2016, 10:45 a.m. - 12:15 p.m.

This dissertation describes theoretical and computational studies of the origin of biological homochirality, and the existence of a liquid-liquid phase transition (LLPT) in pure-component network-forming fluids. A common theme throughout these studies is the use of sophisticated computer simulation and statistical mechanics techniques to study complex condensed-phase phenomena.

In the first part of this dissertation, we use an elementary lattice model to investigate the effect of reaction reversibility on the evolution of chiral-symmetry breaking via autocatalysis and mutual inhibition in a closed system. We identify conditions that facilitate the long-time persistence of a symmetry-broken state, and identify a “monomer purification” mechanism which causes a nearly homochiral state to persist for long times, even in the presence of significant reverse reaction rates.

In part two, we study a chiral-symmetry breaking mechanism known as Viedma ripening. We develop a Monte Carlo model to gain further insights into the mechanisms involved in this process, and provide a comprehensive investigation of how the model parameters impact the system’s overall behavior. We find that size-dependent crystal solubility alone is insufficient to reproduce most experimental signatures, and some form of a solid-phase chiral feedback mechanism (e.g., agglomeration) must be invoked in our model.

In part three, we perform rigorous free energy calculations to investigate the possibility of an LLPT in the Stillinger-Weber (SW) model of silicon, as well as the generalized family of SW models. Contrary to previous findings, our results refute the existence of an LLPT in these models. Explanations for these discrepancies are discussed, along with explicit demonstrations of how these discrepancies may have occurred.

Finally, in part four we perform free energy calculations to demonstrate the existence of an LLPT in the Jagla potential, and calculate the liquid-liquid surface tension. We also investigate the relaxation times of density and bond-orientational order and demonstrate that, contrary to previous assertions, the characteristic relaxation time of bond-orientational order is not orders of magnitude slower than that of density. We compare our results with those published for the ST2 model of water in order to emphasize key similarities and differences between two models which exhibit an LLPT.