Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S27: Focus Session: Solvation of Ions and Electrons II |
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Sponsoring Units: DCP Chair: James M. Lisy, University of Illinois at Urbana-Champaign Room: 204B |
Thursday, March 5, 2015 8:00AM - 8:36AM |
S27.00001: Spectral signatures of large amplitude vibrations in solvated ions. What do the intensities tell us about structure, bonding and dynamics? Invited Speaker: Anne McCoy In this talk, I will discuss recent work in our group in which we made connections between proton transfer processes and hydrogen bonding and vibrational frequencies and intensities. Due to the large amplitude motions associated with proton transfer along a hydrogen bond, the vibrational spectra of these systems contain features that cannot be understood by the usual harmonic description of molecular vibrations. The breakdown reflects both the anharmonicity along this coordinate and coupling between this mode and other low frequency modes in these systems. It also reflects changes in the electronic structure as molecules vibrate. The presentation will draw from reported vibrational spectra for systems either containing intra- or intermolecular hydrogen bonds. Both the theoretical approaches used to study these systems and the insights gained from the studies will be described. The theoretical approaches range from the introduction of higher order terms to the harmonic analysis to adiabatic treatments in which the high- and low-frequency modes are treated at different levels of approximation and diffusion Monte Carlo studies in the full dimensionality of the system of interest. [Preview Abstract] |
Thursday, March 5, 2015 8:36AM - 9:12AM |
S27.00002: Ion Microsolvation Probed by Cryogenic Ion Trap Vibrational Spectroscopy Invited Speaker: Knut R. Asmis How ions are solvated in solution has intrigued physical chemists since the development of the theory of electrolytic dissociation by Arrhenius at the end of the nineteenth century. A molecular-level understanding of ion solvation is not only important for understanding chemical processes in solution, but also plays an important role in understanding the surface speciation and reactivity of aerosols. Infrared photodissociation (IRPD) spectroscopy of mass-selected ions, thermalized to cryogenic temperatures, allows for a detailed characterization of the influence of the stepwise solvation of an ion on its properties, one solvent molecule at a time. Recent advances in the vibrational spectroscopy of atmospherically-relevant microsolvated ions are highlighted, with particular emphasis on using isomer-specific detection schemes and measuring IRPD spectra down into the terahertz region of the electromagnetic spectrum. [Preview Abstract] |
Thursday, March 5, 2015 9:12AM - 9:48AM |
S27.00003: Solvation of ions investigated by DFT-MD simulations: from gas phase to oxide/liquid water interfaces Invited Speaker: Marie-Pierre Gaigeot We investigate the solvation of ions by means of DFT-based molecular dynamics simulations (DFT-MD): ions solvated in clusters and ions solvated at solid oxide/liquid water interfaces. DFT-MD simulations provide a detailed knowledge of the solvation structural properties at finite temperature, and dynamical anharmonic vibrational spectra extracted from DFT-MD are used to detail the relationships between vibrational features and structures. We present recent results for ionic clusters, i.e. solvation of Li$^{\mathrm{+}}$ by water molecules in Li$^{\mathrm{+}}$(H$_{\mathrm{2}}$O)$_{\mathrm{3,4}}$, including dynamical anharmonic vibrational spectra calculations and comparisons to IR-PD (InfraRed Pre-Dissociation) experiments at different temperatures, also including the dynamical formation of these clusters as it occurs in the experiments and the understanding of how high energy conformers can be formed and probed in theses experiments. We also present solvation of electrolytes at the quartz/liquid water interfaces. Here also, not only do we use DFT-MD in order to unravel the structure of these electrolytes at the interface between the oxide and liquid water but we also extract dynamical vibrational spectra to be compared to SFG (Sum Frequency Generation) experiments. With this comparison we aim at a detailed description of the interfacial structure and its related vibrational signatures. \\[4pt] These works have been done in collaboration with Prof J.M. Lisy (USA), Prof M. Sprik (UK), Prof M. Sulpizi (Germany), Dr V. Brites, and M. Pfeiffer. [Preview Abstract] |
Thursday, March 5, 2015 9:48AM - 10:24AM |
S27.00004: Anomalous Vibrational Signatures of Ions and Solvation Invited Speaker: Ryan Steele Vibrational spectroscopy has long served as one of the key experimental windows into the inner workings of molecules. Developments in recent decades have continued to expand these techniques toward exotic ions and biologically relevant systems. Such developments have unearthed a wealth of anomalous vibrational signatures, many of which challenge canonical computational approaches to the simulation of vibrational spectra. In this presentation, the vibrational spectra of particularly challenging ionic systems will be explained via new computational simulations and theoretical frameworks. Examples include (a) strongly anharmonic---yet characteristic---vibrations in protonated, misfolded DNA base pairs, as well as (b) signatures of electronic motion in the vibrational spectra of water oxidation intermediates. Both cases demonstrate strong coupling of a unique electronic structure to quantum mechanical molecular motion. New methodology to enable the interface of these two requirements will also be briefly discussed. [Preview Abstract] |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S27.00005: Modeling ion solvation in ethylene carbonate and propylene carbonate Ayse Arslanargin, Thomas Beck Lithium-ion batteries (LIBs) and supercapacitors are expected to have important roles in renewable energy generation and in electric vehicles as electrochemical storage systems. Non-aqueous solvents such as ethylene carbonate (EC), and propylene carbonate (PC) are widely used as liquid electrolytes in LIBs. The electrolyte structure affects the efficiency of the ion transport, and understanding the solvent structure is essential for battery performance enhancements. This work investigates the thermodynamics of ion solvation in EC and PC. Free energy and enthalpy of solvation calculations have been conducted employing different force fields. Simulated annealing calculations have been performed to fit classical ion-solvent dimer interaction energies to quantum data. Non-bonded energy parameters are altered during the fitting process. The new parameters result in good agreement with the experimental free energy of solvation values, while the enthalpy of solvation results show deviations from the experimental data. These results suggest that classical models often do not accurately predict basic interactions in ion-solvent systems. [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S27.00006: Mechanisms of Li-ion transport in bulk electrolytes and through solid-electrolyte interphases (SEI) Dmitry Bedrov, Zhe Li, Oleg Borodin Performance of Li-ion batteries is strongly coupled to the mechanisms of Li$^{+}$ transport in bulk electrolytes, its transition through electrolyte/SEI interface and its transport through glassy SEI matrix. We will discuss the results of extensive atomistic molecular dynamics (MD) simulations using APPLE{\&}P polarizable force field and that have focused on understanding of correlations between the Li$^{+}$ local structure and the mechanisms of Li$^{+}$ transport in these systems. Specifically, we will address: a) Li$^{+}$ transport in ionic liquid based electrolytes and the influence of organic solvent additives (ethylene carbonate and acetonitrile), b) Li-ion transport through model SEIs comprised of alkyl dicarbonate anions and the influence of SEI contamination by Mn$^{2+}$ cations, and c) transition of Li$^{+}$ ions through SEI/electrolyte interfaces. [Preview Abstract] |
Thursday, March 5, 2015 10:48AM - 11:00AM |
S27.00007: Understanding Complex Ion Dynamics in Lithium-Ion Battery Electrolytes from First Principles Mitchell Ong, Vincenzo Lordi, Timo Bremer, Attila Gyulassy, Erik Draeger, Harsh Bhatia, John Pask Lithium-ion secondary batteries are commonly used to power many consumer devices such as handheld phones, laptops, portable music players, and even electric vehicles. One of the key properties that influence the performance of lithium-ion batteries is the ionic conductivity of the electrolyte. This is dependent on the mobility of the Li ion in solution and also related to their solvation structure. In this work, we have performed first principle molecular dynamics of an LiPF$_{\mathrm{6}}$ salt solvated in different organic solvents such as ethylene carbonate (EC), ethyl methyl carbonate (EMC) and a mixture of the two. We observed that the diffusivity of Li$^{\mathrm{+}}$ is correlated to the degree of Li$^{\mathrm{+}}$ solvation. Corresponding analysis for PF$_{\mathrm{6}}^{\mathrm{-}}$ shows greater diffusivity than Li$^{\mathrm{+}}$ associated with a weakly-bound, poorly defined first solvation shell. Using a recent analysis method to study the distribution of directional change from relative angles at successive time intervals, we also characterize the complex motion of these ions and find distinct patterns for each ion in different organic solvents. These results provide valuable insight that can be used to improve the cycling rate of Li-ion batteries and potentially lead to the design of new electrolytes for better overall battery performance. [Preview Abstract] |
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