Bulletin of the American Physical Society
2018 Annual Meeting of the APS Mid-Atlantic Section
Volume 63, Number 20
Friday–Sunday, November 9–11, 2018; College Park, Maryland
Session F02: Chemical Physics II |
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Chair: Amy Mullin, University of Maryland, College Park Room: Edward St. John 1215 |
Saturday, November 10, 2018 1:30PM - 2:06PM |
F02.00001: Three birds with one stone: reaction coordinate, thermodynamics and kinetics from all-atom molecular simulations Invited Speaker: Pratyush Tiwary Many molecular systems involve processes with intertwined spatio-temporal resolutions ranging from femtoseconds to days, making it hard to probe them completely using traditional experimental tools. It has been a holy grail to simulate these in all-atom resolution using molecular dynamics methods, but these can go up to only a few hundred microseconds even with the most powerful and custom-built supercomputers. Thankfully, over the decades several sampling algorithms have been proposed that can simulate these complex systems in an accelerated but controllable manner. However, a large class of these methods (arguably all!) need an a priori sense of a low-dimensional reaction coordinate (RC) even before performing the sampling. This has severely limited the usefulness of such sampling methods. In order to deal with this cyclic problem where one needs extensive sampling of the rare events to know the RC, but also needs to know the RC in the first place to perform sampling, it is thus extremely desirable to construct methods that learn the RC as they perform the sampling. Here we will describe two such methods, namely SGOOP [1] and RAVE [2] developed by us that use flavors of statistical mechanics and deep learning to solve this problem. We will demonstrate the generality and power of these methods by showing how they give direct predictive insight into different biologically important problems such as mechanisms of ligand-protein and transcription factor-DNA interactions. Our findings includes an all-atom characterization of metastable and transition states, their stabilities, various rate constants, as well as prediction of deleterious point mutations in the system which could upend the functioning of the protein, DNA or the ligand. [1] Tiwary and Berne, Proc. Natl. Acad. Sci. 113, 2839-2844 (2016) [2] Ribeiro, Bravo, Wang, Tiwary, J. Chem. Phys. 149, 072301-072309 (2018) |
Saturday, November 10, 2018 2:06PM - 2:18PM |
F02.00002: Carbon Nanofibers as Conductive Additive in LiFePO4 Cathode Material for Li-ion Batteries Adewale Adepoju, Quinton Williams Olivine LiFePO4 is one of the leading candidates for Li-ion batteries cathode materials because of its stable structure, nontoxicity, and relatively low cost. However, LiFePO4 has poor electronic conductivity and slow Li-ion diffusion rate. Different approaches have been established to address this problem. In this work, we address the problem of poor electronic conductivity by incorporating carbon nanofibers (CNFs) into the LiFePO4 cathode as conductive additives. CNFs have a high aspect ratio and excellent electronic conductivity via its reactive inner and outer surface structure. The effect of adding different weight percentages of CNFs to the LiFePO4 cathode was investigated by scanning electron microscope (SEM), four-point probe, and electrochemical measurements. Practically, the composite cathode with 5 wt.% CNFs showed enhanced electrochemical properties in terms of the rate performance, cycling capacity, and capacity retention. The improved electrochemical performance is attributed to the better electronic percolation networks that were created by adding CNFs. |
Saturday, November 10, 2018 2:18PM - 2:30PM |
F02.00003: Dielectric Relaxation of Gaussian-smoothed Solutes Renjie Zhao, John D Weeks The dielectric solvation dynamics of charged solutes is investigated for models with slowly-varying continuous charge densities. We describe the dielectric effects of Gaussian-smoothed ionic and dipolar solutes by assuming a linear response induced in the solvent. Empirical dielectric functions, such as Debye relaxation function, are employed to derive the relaxation time of the considered models. We suggest a mathematical framework incorporating both Gaussian-smoothed and classic models to predict the dielectric and relaxation behavior of dipoles. |
Saturday, November 10, 2018 2:30PM - 3:06PM |
F02.00004: Complex kinetics of ion solvation in confinement and in bulk Invited Speaker: Richard C Remsing Traditional pictures of solution phase chemistry and biology treat the surrounding solvent as a spectator. However, in recent years, it has been shown that the solvent can be a key player in condensed phase chemical dynamics. In this talk, I will discuss the non-trivial role of the solvent in two fundamental chemical reactions involving ions, electron transfer and solvent exchange. These processes play important roles in energy conversion and storage technologies, geochemistry, and biophysics. I will first discuss ion solvation dynamics surrounding electron transfer reactions in solutions confined within layered transition metal oxide minerals, with an emphasis on guiding principles for catalysis. The interplay between confinement and ion solvation leads to unique structures and dynamics of water molecules that enhance electron transfer rates. This enhancement is explained with an extension of the XY model, creating an analogy to magnetic materials. I will also discuss the complex, facilitated dynamics of water exchange around ions. In particular, the extreme sensitivity of exchange rates to perturbations in the chemistry of an ionic solute is not well understood. By borrowing concepts from the physics of glassy systems, I will demonstrate how the scaling of exchange rates with ion-water interaction strength can be predicted with the help of kinetically-constrained lattice models. |
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