Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session L16: Aqueous Solutions, Solvated Interfaces, and Ionic Polarization IIFocus Session
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Sponsoring Units: DCOMP DCP Chair: Jeffrey Greeley, Purdue University Room: BCEC 155 |
Wednesday, March 6, 2019 11:15AM - 11:51AM |
L16.00001: Unraveling correlation effects in water from microscopic response functions Invited Speaker: Deyu Lu Electronic correlation effects play a crucial role in determining the structural and chemical properties of water. Over past decades, first-principles theory has been widely used to obtain physical insights of water and interpret experimental results. However, direct analysis of the electronic correlation in water from first principle is non-trivial, which motivates the development of new descriptors based on the microscopic response functions and formal methodologies to efficiently evaluate them. Recently, we have developed an ab initio local dielectric response theory [Phys. Rev. B 92, 241107, 2015] that partitions the microscopic electric susceptibility in real space based on the Wannier representation. Several applications of the local dielectric response theory are discussed. We demonstrate how to compute the molecular polarizability of water in the condensed phase and analyze the effects of the hydrogen-bonded network resulting from the crystal field and charge transfer. In another example, we studied the non-local correlation behaviors between water and solvated ions, and identified different screening characteristics of longitudinal and transverse modes. |
Wednesday, March 6, 2019 11:51AM - 12:03PM |
L16.00002: Tracking holes and their reactivity in photon-driven reactions using Real-Time Time-Dependent Density Functional Theory (RT-TDDFT) Vidushi Sharma, Marivi Fernandez Serra Photocatalytic reactions on semiconductor surfaces that produce hydrogen have the potential of addressing our growing energy needs. However, the possible reaction intermediates and trajectories associated with such photon-driven reactions are currently not well understood. Our aim is to study the response of molecular systems upon photoexcitation. We are particularly interested in the evolution of a system on the excited-state potential energy surface and the interaction of the molecular intermediates with its surroundings after excitation which leads to the desired reaction. We use ab initio nonadiabatic simulations to study the time evolution of photoexcited states, and we simulate the coupled electron-ion dynamics using RT-TDDFT-based Ehrenfest dynamics. This is a promising nonadiabatic dynamics scheme given the considerable sizes of the molecular systems of interest. We compare the ultrafast dynamics of the ``photogenerated-hole'' as captured by RT-TDDFT Ehrenfest dynamics with the commonly used Born-Oppenheimer dynamics at similar time scales and identify the key physical characteristics that differentiate one from the other, thereby empirically testing a more computationally intensive nonadiabatic scheme for elucidating the physics of photoexcited systems. |
Wednesday, March 6, 2019 12:03PM - 12:15PM |
L16.00003: Energy fluctuations in water: How are they coupled to protein dynamics and vice versa? Saumyak Mukherjee, Sayantan Mondal, Biman Bagchi The exotic properties of water have intrigued researchers over a long time. Aqueous solutions of complex biomolecules like proteins trigger further interest. Several theories address the complexity of protein-water interactions. Frauenfelder et al. hypothesized the solvent slaving of protein dynamics. In this work, for the first time, we propose a mechanistic pathway of such protein-water coupling. Using atomistic molecular dynamics simulations on five proteins, we find that water dipoles efficiently interact with polar groups at the protein core. The forces thus experienced are comparable to the forces of interaction with other protein atoms. We also find that the fluctuations in self-energy of protein are significantly anti-correlated to the fluctuations in protein-water interaction energy. This signifies a microscopic channel of energy flow between protein and water. This coupling is also manifested in the total energy spectrum of protein which shows bimodal 1/f noise characteristics. The additional slope in the spectrum shows signature of perturbation from water as shown by Ohmine et al. |
Wednesday, March 6, 2019 12:15PM - 12:27PM |
L16.00004: Multiscale modeling of systems with confined electrolytes Francisco Solis Macroscopic models of physiological materials describe often tissues as passive homogeneous electric materials. At the mesoscopic level, these materials are typically composed of cells or other structures of similar scale which can be considered as confined electrolytes. Conduction and polarization of these structures can be effectively described by means of density functional theories. In this presentation it will be shown how computations for confined electrolytes can be used to build effective macroscopic models. In particular, we interpret the macroscopic conductivity and polarizability in terms of the properties of the confined electrolytes, analyzed by means of dissipative dynamics. |
Wednesday, March 6, 2019 12:27PM - 12:39PM |
L16.00005: Salt Ion Transport Through Carbon Nanotubes: Insights from Polarizable Force Field-Based Molecular Dynamics Simulations Rahul Prasanna Misra, Daniel Blankschtein Carbon Nanotubes (CNTs) which are cylindrical 1D allotropes of carbon are emerging as promising materials for membrane-based applications, including seawater desalination and osmotic power harvesting. For the rational design of CNTs in membrane-based applications, it is imperative to develop a fundamental understanding of the interactions of salt ions such as Na+ and Cl- with the carbon atoms of CNTs. Given the large polarizability tensors of CNTs, salt ions inside CNTs can exert strong electric fields which can result in a significant polarization of the CNTs. Although the ion – CNT polarization energy is high (e.g., 27 kcal/mol inside a 0.8 nm diameter CNT) and makes the dominant contribution to the ion - CNT binding energy, previous MD simulation studies have neglected the polarization of CNTs in the presence of water molecules and salt ions. In this talk, we discuss our formulation of polarizable force fields parameterized using quantum chemical simulations which can self-consistently model the anisotropic polarizability tensors of CNTs, as well as reliably model water-CNT and ion-CNT interactions. Finally, by performing classical MD simulations with polarizable force fields, we carry out a comprehensive investigation of salt ion transport through 0.8 – 2 nm diameter CNTs. |
Wednesday, March 6, 2019 12:39PM - 12:51PM |
L16.00006: Cation-specific effects on the attraction of anions to a hydrophobic surface Travis Douglas, Miaoqi Chu, Sangjun Yoo, Chung-Jong Yu, Pulak Dutta Halides such as bromide and iodide are known to accumulate near the free surface of an electrolyte solution. Solid hydrophobic surfaces in contact with water induce a density-depleted gap near the interface, creating a water density profile similar to the free surface. It is therefore possible that polarizable ions like halides are also attracted to hydrophobic surfaces, a notion that is supported by MD simulations. However, the buried solid-liquid interface is more difficult to access experimentally than the free surface of water and is thus much less studied. We present results of an x-ray reflectivity study of aqueous alkali metal-iodide solutions in contact with a hydrophobic self-assembled monolayer. A layer of enhanced anion density is observed at the SAM-water interface, but with an unexpected strong dependence on the cation present in the solution. This experiment attempts to provide insight into the less understood yet ubiquitous interactions between ions and real hydrophobic/non-polar materials, such as proteins and organic materials present in the atmosphere and soil. |
Wednesday, March 6, 2019 12:51PM - 1:03PM |
L16.00007: Protonation of headgroups of fatty amines in Langmuir monolayer controlled by surface density Sona Krem, Minho Lee, Sokhuoy Sam, Woongmo Sung, Doseok Kim Charge status of the headgroups of the molecules consisting monolayer at different area per molecules is studied by sum-frequency vibrational spectroscopy. Langmuir monolayers consisting of mixtures of 1-hexadecanol (HD) and octadecyl amine (ODA) molecules at different molar ratios were prepared to investigate the effect of surface area/molecule on the charge status of the amine headgroup. Here the fatty alcohol molecules worked as mere spacers to widen the distance between the amine groups. Sum-frequency vibrational spectra in the OH range was larger for the monolayers having intermediate area/molecule, which indicated the surface is more charged even when there are less amine groups in the monolayer. To compare with the above systems, 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP), a surfactant molecule having quaternary amine headgroup was then mixed with 1-hexadecanol (HD) at different molar ratios and investigated by SFVS. Comparison of the OH spectral areas of HD/ODA and HD/DPTAP systems allowed quantitative estimation of the protonation fraction of amine headgroups in the ODA mixture monolayers. Gouy–Chapman theory that took into account the area change followed the observed trend on the protonation of the amine headgroup. |
Wednesday, March 6, 2019 1:03PM - 1:15PM |
L16.00008: First-Principles Study of the Solvation Structure of Tetraglyme based Electrolytes Yang Sun, Ikutaro Hamada Glyme based electrolytes for rechargeable Li secondary batteries are of great interest, due to the high oxidative stability, low vapor pressure, and non-flammability. Here we employ the first-principles molecular dynamics simulation to study the lithium bis(trifluoromethylsulfonyl)-amide (LiTFSA) and tetraglyme (G4) electrolyte system. For the case of equimolar Li salt concentration, a positive correlation between the total coordination number of Li+ ions and the phase stability is clearly established. At the ground state of equimolar LiTFSA-G4 electrolyte, most of Li+ ions are coordinated to four O atoms of a curled G4 molecule and one O atom of a TFSA− anion. By contrast, Li+ ions prefer to be coordinated by two G4 molecules and not in direct contact with TFSA− anions at a low concentration of the Li salt. The significantly increased probability of pairing between the Li-G4 complexes and TFSA− anions at the equimolar ratio could be highly relevant to its ionic-liquid-like properties [1]. |
Wednesday, March 6, 2019 1:15PM - 1:27PM |
L16.00009: Ionic Structure in Highly-Concentrated Confined Electrolytes Nasim Anousheh, Francisco Solis, Vikram Jadhao Recent surface force measurements have shown that the effective force between mica surfaces does not decay as sharply as predicted by mean-field models such as the Debye-Huckel theory when the concentration of the confined electrolytes is high (around 2 M for NaCl). In other words, the interaction between charged surfaces is “under-screened” at high electrolyte concentrations. Motivated by these experiments, we use molecular dynamics simulations and strong coupling theory to extract the ionic structure in aqueous NaCl electrolytes confined by two interfaces. Ionic density profiles, effective force (pressure) between surfaces, and pair correlation functions are extracted for electrolytes confined between uncharged, charged, and polarizable interfaces at different concentrations (0.1 M to over 2 M). Effects of varying ion sizes, surface separation, and dielectric properties of the solvent are outlined. Simulation results are correlated with strong coupling theory calculations where “underscreening” behavior is associated with the formation of highly correlated groups of ions that act as individual entities. |
Wednesday, March 6, 2019 1:27PM - 1:39PM |
L16.00010: Examining Electronic Excitations in Liquid Water under Proton and Photon Irradiation Chris Shepard, Dillon C. Yost, Yi Yao, Yosuke Kanai Proton and Photon irradiation of liquid water is important in many areas of modern technology, including cancer beam therapies. However, understanding the molecular level details of induced electronic excitation has been elusive. Using real-time time-dependent density functional theory, we study the dynamics of electron excitation in liquid water through the propagation of maximally-localized Wannier functions (MLWFs). The MLWF dynamics provide a convenient “molecular orbital” picture of the electronic structure, to understand electronic excitation in terms of localized electrons. We examine the extent to which photo-excitation and electronic stopping excitation differ at the molecular level. |
Wednesday, March 6, 2019 1:39PM - 1:51PM |
L16.00011: TDDFT approach on laser field enhancement by carbon nanotube and photo-decomposition of water
Hong Zhang1, Yoshiyuki Miyamoto2, Xinlu Cheng1, Angel Rubio3
1College of Physical Science and Technology, Sichuan University, Chengdu 610065, China
Hong Zhang
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Wednesday, March 6, 2019 1:51PM - 2:03PM |
L16.00012: A Molecular Dynamics Study of Ion Separation and Water Purification Using Graphene/Carbon Nanotube Filter Samaneh Rikhtehgaran, Luc T Wille Molecular dynamics (MD) simulations have been used to design a graphene carbon nanotube (CNT) filter with an efficiency greater than 90% to separate Na+ and Cl- ions from water molecules. The results show that the magnitude of the charge density that covers the surface of the CNT can noticeably influence the performance of ion separation and water purification. Therefore, the ion separation is improved by increasing the magnitude of the surface charge density enormously. In addition, it is observed that the velocity of the piston can have a huge impact on the filter’s performance. This work establishes an atomic-level understanding of the effects of graphene and nanostructures on desalination and can be helpful for designing new nanofilter. |
Wednesday, March 6, 2019 2:03PM - 2:15PM |
L16.00013: K-shell Core Electron Excitations in Electronic Stopping of Protons in Water from First Principles Yi Yao, Dillon C. Yost, Yosuke Kanai Understanding the role of core electron excitations in liquid water under proton irradiation has become increasingly important due to the growing use of ion beams in radiation oncology as an alternative to the X/γ-ray photon radiation. Using a first-principles, non-equilibrium simulation approach based on real-time TDDFT, we accurately determine the electronic stopping power over a wide range of proton velocities. The result agrees with available experimental data and also with the SRIM model. Explicit treatment of the K-shell, 1s electrons of oxygen atoms in water was found to be necessary to accurately predict the electronic stopping power for large velocities. The simulations also reveal that excitations of K-shell core electrons influence the valence electron excitation itself, and the separate treatment of valence and core electron excitation is not satisfactory for large velocities. |
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