Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session T42: Focus Session: Supercooled and Nanoconfined Water II |
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Sponsoring Units: DCP Chair: Anders Nilsson, SLAC Room: Hilton Baltimore Holiday Ballroom 3 |
Thursday, March 21, 2013 8:00AM - 8:36AM |
T42.00001: Supercooled aqueous solutions: a route to explore water anomalies Invited Speaker: Paola Gallo In the past years several theoretical and experimental studies have led to a picture according to which the anomalous properties of water might be due to the presence of a liquid-liquid phase transition in the supercooled region possibly terminating in a liquid-liquid critical point, LLCP [1]. I will show molecular dynamics simulations results of ionic aqueous solutions [2,3,4] and of a solution of water and methanol [5] aimed to clarify the effect of these species on water anomalies and the LLCP phenomenon. I will focus on the phase diagram of water in the supercooled region of the solutions in comparison with the bulk to quantify the modifications induced by the presence of the solutes. I will show that the LLCP phenomenon persists for concentrations from low to moderate and that experimental measurements appear easier for solutions. I will also show how indications of the presence of a LLCP nearby can come not only from thermodynamics but also from crossovers in dynamics [6,7] and from the two-body excess entropy behavior [8] as calculated from the structure [9]. I will in particular show that, similar to the bulk, the transition from a fragile behavior to a strong behavior of the liquid is present also in solutions and it is connected to the LLCP phenomenon. These studies point out that experiments in solutions are extremely relevant for the comprehension of low temperature bulk water properties. \\[4pt] [1] P. H. Poole, F. Sciortino, U. Essmann and H. E. Stanley, Nature 360, 324 (1992)\\[0pt] [2] D. Corradini, M. Rovere and P. Gallo, J. Chem. Phys. 132, 134508 (2010)\\[0pt] [3] D. Corradini and P. Gallo, J. Phys. Chem. B. 115, 14161 (2011)\\[0pt] [4] P.Gallo, D. Corradini and M. Rovere, Phys. Chem. Chem. Phys. 13, 19814 (2011)\\[0pt] [5] D. Corradini, Z. Su, H.E. Stanley and P. Gallo J. Chem. Phys. 187, 184503 (2012).\\[0pt] [6] P. Gallo and M. Rovere, J. Chem. Phys. 137, 164503 (2012)\\[0pt] [7] P. Gallo, D. Corradini and M. Rovere, in preparation (2013)\\[0pt] [8] P. Gallo, D. Corradini and M. Rovere, Mol. Phys, 109, 2069 (2011)\\[0pt] [9] D. Corradini, M. Rovere and P. Gallo, J. Phys. Chem. B, 115, 1461 (2011). [Preview Abstract] |
Thursday, March 21, 2013 8:36AM - 8:48AM |
T42.00002: Probing the Structure of Salt Water Under Confinement with Computation Heather Kulik, Eric Schwegler, Giulia Galli We have investigated the structure of liquid water around cations (Na$^+$) and anions (Cl$^-$) confined inside a (19,0) carbon nanotube with first principles molecular dynamics (FPMD) and theoretical X-ray absorption spectroscopy (XAS). We study the distribution of ions and nature of the ion solvation shells under confinement from molecular dynamics. We also examine the XAS signal of water molecules surrounding Na$^+$ and Cl$^-$ upon confinement and relate these spectral fingerprints to those of solvated ions in bulk water. We observe unusual trends in the XAS upon confinement of cations and anions that likely stems from variation in the number of acceptor hydrogen bonds in the first solvation shell for the two species. The rigid first solvation shell of Na$^+$ is rigid whether in bulk or confined solution, disrupting the overall hydrogen bonding network of the rest of the confined water. The solvation shell of Cl$^-$ is considerably more flexible and adapts under confinement to accommodate roughly the same number of acceptor bonds. In our nanotube, we observe an inner bulk-like shell of water and outer shell of interfacial waters, as observed through both FPMD and XAS properties. [Preview Abstract] |
Thursday, March 21, 2013 8:48AM - 9:00AM |
T42.00003: ABSTRACT WITHDRAWN |
Thursday, March 21, 2013 9:00AM - 9:12AM |
T42.00004: Electric Field Fluctuations in Water Dayton Thorpe, David Limmer, David Chandler Charge transfer in solution, such as autoionization and ion pair dissociation in water, is governed by rare electric field fluctuations of the solvent. Knowing the statistics of such fluctuations can help explain the dynamics of these rare events. Trajectories short enough to be tractable by computer simulation are virtually certain not to sample the large fluctuations that promote rare events. Here, we employ importance sampling techniques with classical molecular dynamics simulations of liquid water to study statistics of electric field fluctuations far from their means. We find that the distributions of electric fields located on individual water molecules are not in general gaussian. Near the mean this non-gaussianity is due to the internal charge distribution of the water molecule. Further from the mean, however, there is a previously unreported Bjerrum-like defect that stabilizes certain large fluctuations out of equilibrium. As expected, differences in electric fields acting between molecules are gaussian to a remarkable degree. By studying these differences, though, we are able to determine what configurations result not only in large electric fields, but also in electric fields with long spatial correlations that may be needed to promote charge separation. [Preview Abstract] |
Thursday, March 21, 2013 9:12AM - 9:48AM |
T42.00005: Solute effects on the thermodynamic and kinetic behavior of water and liquid-liquid transition Invited Speaker: Hajime Tanaka Water is known to be an exceptionally poor glass former, which is one of the characteristic features of water, but its link to the thermodynamic and kinetic anomalies of water remains elusive. Recently we showed that the glass-forming ability and the fragility of a water/salt mixture are closely related to its equilibrium phase diagram.\footnote{M. Kobayashi and H. Tanaka, Phys. Rev. Lett. {\bf 106}, 125703 (2011);J. Phys. Chem. B {\bf 115}, 14077 (2011)} We proposed that frustration between local and global orderings controls both the glass-forming ability and fragility on the basis of experimental evidence. Relying on the same role of salt and pressure, which commonly breaks tetrahedral order, we apply this idea to pure water under pressure. This scenario not only explains unusual behavior of water-type liquids such as water, Si and Ge, but also provides a general explanation on the link between the equilibrium phase diagram, the glass-forming ability, and the fragility of various materials including oxides, chalcogenides, and metallic glasses.\footnote{H. Tanaka, Eur. Phys. J. E {\bf 35}, 113 (2012)} We also discuss liquid-liquid transition found in mixtures of water with glycerol\footnote{K. Murata and H. Tanaka, Nature Mater. {\bf 11}, 436 (2012)} and other molecules and its implications. [Preview Abstract] |
Thursday, March 21, 2013 9:48AM - 10:00AM |
T42.00006: Local Environment Distribution in Ab Initio Liquid Water Biswajit Santra, Robert A. DiStasio, Jr., Roberto Car We have analyzed the distribution of local environments in liquid water at ambient conditions and its inherent potential energy surface (IPES) based on state-of-the-art {\it ab initio} molecular dynamics simulations performed on 128 molecules implementing hybrid PBE0 exchange [PRB {\bf 79}, 085102 (2009)] and van der Waals (vdW) interactions [PRL {\bf 102}, 073005 (2009)]. The local environments of molecules are characterized in terms of the local structure index (LSI) [JCP {\bf 104}, 7671 (1996)] which is able to distinguish high- and low-density molecular environments. In agreement with simulations based on model potentials, we find that the distribution of LSI is unimodal at ambient conditions and bimodal in the IPES, consistent with the existence of polymorphism in amorphous phases of water. At ambient conditions spatial LSI fluctuations extend up to $\sim$7 \AA\ and their dynamical correlation decays on a time scale of $\sim$3 ps, as found for density fluctuations in a recent study [PRL {\bf 106}, 037801 (2011)]. [Preview Abstract] |
Thursday, March 21, 2013 10:00AM - 10:12AM |
T42.00007: Connexions between density and dielectric properties of water Luana Pedroza, Daniel Elton, Marivi Fernandez-Serra As it is well known, water has a high dielectric constant, which is connected both to the molecular dipole moment and to the intermolecular bonding through hydrogen bonds. Although some classical force fields can reproduce this dielectric constant, they do not take into account the environment-dependent perturbations of the individual dipoles and their relation to the local structure and network of the liquid. In this work, we investigate in detail the distribution of molecular dipoles for different densities of liquid water, obtained with ab initio molecular dynamics simulations and compare them to those obtained using a classical, polarizable, empirical force field. We calculate the dipole moment for different choices of exchange-correlation functionals, including van der Waals correction. In addition, we analyze the correlation between the dipolar coupling and the vibrational spectrum of water. In this way, we can get a better understanding on how local electronic effects play a role in the determination of global properties of water, such as its dielectric constant and density [Preview Abstract] |
Thursday, March 21, 2013 10:12AM - 10:24AM |
T42.00008: Quantum Zero Point Effects in Water and Ice Bet\"{u}l Pamuk, Marivi Fern\'andez-Serra Nuclear zero point effects have recently been shown to have an interesting quantum anomaly in ice. In particular, In hexagonal ice Ih, the lattice volume increases when H is replaced by D. This anomalous isotope shift of the lattice parameter increases with temperature, contrary to normal expectations [1]. Free energy calculations within the quasiharmonic approximation, with \textit{ab initio} density functional theory, explain the origin of his anomaly. In this study, we extend our study to show that the anomalous isotope effect persists in amorphous ices, inherent structures of liquid water. This indicates that the anomalous isotope effect on the density of liquid water might be intrinsically related to the one observed in ice, even if their structures are radically different. In addition, we show that clathrate hydrides, also have this anomaly. We make a detailed analysis of the origin of the anomaly and study how the Hbond interaction and the vdW bond in liquid water are modified by these nuclear zero point effects. [1] B. Pamuk \textit{et. al}, Phys. Rev. Lett. \textbf{108}, 193003 (2012). [Preview Abstract] |
Thursday, March 21, 2013 10:24AM - 10:36AM |
T42.00009: First-Principles Investigation of Water Properties at Functionalized Silicon surface Donghwa Lee, Eric Schwegler, Yosuke Kanai Numerous experimental and theoretical investigations have been made to understand the behavior of water molecules under various conditions. Interfacial water behavior at semiconductor interfaces is one of the most important areas of investigation for diverse industrial applications such as crystal growth, lubrication, catalysis, electrochemistry and sensors. Although the terms, hydrophobic and/or hydrophilic, are often used to describe the properties of water in this context at macroscopic level, the effect of hydrophobicity on water behavior at nano-scale interfaces is still not well understood. Computational simulations could offer atomistic basis to build a better foundation for understanding this important dynamics. In this study, first principles molecular dynamics is employed to investigate the water behavior at silicon surfaces that are functionalized with several different molecules. In particular, various analysis methods are used to elucidate the effect of surface polarity on structural and dynamical properties of interfacial water. Our studies show that properties of interfacial water are not always governed by surface polarity alone but also by other atomistic factors. [Preview Abstract] |
Thursday, March 21, 2013 10:36AM - 10:48AM |
T42.00010: Anatomy of competing quantum effects in liquid water. Rafa Ramirez, Sriram Ganeshan, M. V. Fernandez-Serra ct- Molecules like water have vibrational modes with zero point energy well above room temperature. As a consequence, classical molecular dynamics simulations of liquid water largely underestimate the kinetic energy of the ions, which translates into an underestimation of covalent interatomic distances. In this work, we show that it is possible to apply generalized Langevin equation with suppressed noise in combination with Nose-Hoover thermostats to achieve an efficient zero-point temperature of independent modes of liquid water. Using this method we deconstruct the competing quantum effects in liquid water. We demonstrate how the structure and dynamical modes of liquid water respond to non-equilibrium distribution of zero point temperatures on the normal modes. [Preview Abstract] |
Thursday, March 21, 2013 10:48AM - 11:00AM |
T42.00011: The role of water in surface charge transport on tin dioxide as revealed by the thermal dependence of conductance Robert Wexler, Karl Sohlberg The presence of water on an oxide surface can dramatically alter its electrical properties with important consequences for electrical measurements by scanning probe microscopy, and for the use of semiconducting oxides in sensing applications. Here, the thermal dependence of the surface conductance of tin dioxide is interpreted by combining equilibrium carrier statistics with the Grotthuss mechanism for proton hopping. The functional form of this charge transport model is fit to experimental conductance data for tin dioxide. Next, the important energy parameters in the model are computed with electronic structure methods. Comparing the values of the energy parameters obtained by fitting to those obtained from electronic structure calculations yields new insight into the surface charge transport in tin dioxide. In particular, it is found that mobile protons, freed by the dissociative adsorption of water on the [110] surface, are an essential component of the observed thermal dependence of surface conductance in tin dioxide. [Preview Abstract] |
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