Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session B6: Theoretical and Computational Studies of Water |
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Sponsoring Units: DCOMP Chair: Giulia Galli/LLNL Room: LACC 502A |
Monday, March 21, 2005 11:15AM - 11:51AM |
B6.00001: X-ray Absorption Spectroscopy and Electronic Structure Calculations of Water and Ice Invited Speaker: We have investigated the electronic structure of water and ice using a combination of experimental and theoretical techniques [1]. Measurements have been performed on the liquid using both X-ray Absorption (XAS) and X-ray Raman Spectroscopy. The spectrum of the liquid is distinctly different from that of tetrahedrally coordinated bulk ice, where the liquid shows a distinct pre-edge feature and a strong enhancement of the intensity at the edge. Through spectrum simulations and model experiments (bulk and surface of ice) we show that the specific features in the liquid spectrum are due exclusively to asymmetric configurations with only two strong hydrogen bonds: one donating and one accepting [1]. Here I will discuss the interpretation of the spectra on the basis of theoretical modeling using both cluster and periodic plane-waves techniques together with the various approximations involved. In [1] the appearance of the specific features in the liquid spectrum was shown to be represented by a cone-criterion for the donating H-bonds: one with the accepting molecule inside and the other outside the cone. This is a necessary, but not sufficient criterion to predict the pre-edge. From a very large number of models studied we can derive more stringent conditions on the local structure, which indicate more directly what type of configurations that are under-represented in dynamics simulations compared with experiment. Compton scattering measures the electronic momentum distribution. It is sensitive to intermolecular H-bond distances and the associated intramolecular O-H bond changes. I will discuss the theoretical implementation of this spectroscopy and show how it can be used to obtain further insight into the local structure of the liquid. [1] Wernet et al, Science \textbf{304}, 995-999 (2004) [Preview Abstract] |
Monday, March 21, 2005 11:51AM - 12:27PM |
B6.00002: Super-cooled and glassy water and liquid-liquid phase transitions: a computer simulation perspective Invited Speaker: |
Monday, March 21, 2005 12:27PM - 1:03PM |
B6.00003: Ab-initio simulations of liquid water: dielectric and hydrophobic effects Invited Speaker: Hydrogen bonds are at the origin of many special properties of water. In this talk I will show how extensive \textit{ab-initio} molecular dynamics simulations and simple theoretical models give insight on the structure and dynamics of the H-bond network. I will discuss in particular: (a) a study of the dielectric properties of water, based on simulations under a finite applied electric field, and (b) a study of the molecular origin of the hydrophobic effect, based on simulations of a solvated methane pair. [Preview Abstract] |
Monday, March 21, 2005 1:03PM - 1:39PM |
B6.00004: Structural and dynamical properties of water under ambient and high-pressure conditions Invited Speaker: The structural and dynamical properties of water are investigated with \textit{ab initio} molecular dynamics. A series of density functional theory based simulations is presented where the effect of temperature at ambient density is explored in order to demonstrate the level of accuracy that can be achieved, and the open challenges that remain in describing liquid water [1,2]. In addition to water at ambient density, the effect of high-pressures, in a regime where molecular dissociation plays a dominant role, is explored for both liquid water and the high-pressure phases of ice. In particular, large-scale two phase simulations of water are used to determine the melting temperature of water in the range of 10 to 50 GPa [3]. This work was performed under the auspices of the US Department of Energy by the University of California at the LLNL under contract no W-7405-Eng-48. * In collaboration with Jeffery C. Grossman, Fran\c{c}ois Gygi and Giulia Galli. [1] ``Towards an assessment of the accuracy of density functional theory for first principles simulations of water'', J. Grossman, E. Schwegler, E. Draeger, F. Gygi and G. Galli, \textit{J. Chem. Phys.} \textbf{120}, 300 (2004); and ``Towards an assessment of the accuracy of density functional theory for first principles simulations of water II'', E. Schwegler, J. Grossman, F. Gygi and G. Galli, \textit{J. Chem. Phys.} \textbf{121}, 5400 (2004). [2] ``First principles simulations of rigid water'', M. Allesch, E. Schwegler, F. Gygi and G.Galli, \textit{J. Chem. Phys}. \textbf{120}, 5192 (2004). [3] ``Dissociation of water under pressure''$, $E. Schwegler, G. Galli, F. Gygi, and R. Hood, \textit{Phys. Rev. Lett.} \textbf{87,} 265501 (2001); and E. Schwegler, F. Gygi and G. Galli (manuscript in preparation). [Preview Abstract] |
Monday, March 21, 2005 1:39PM - 2:15PM |
B6.00005: Proton Solvation and Transport in Aqueous Environments Invited Speaker: The solvation and transport of excess protons in several important systems will be described using the multi-state empirical valence (MS-EVB) approach combined with large scale molecular dynamics (MD) simulation. The MS-EVB approach allows for the treatment of explicit proton shuttling (dynamical bond-breaking), which, in turn, strongly influences the properties of excess protons in various aqueous environments. Proton solvation and transport in bulk water, water clusters, the water liquid-vacuum interface, and water-filled channels will be discussed. [Preview Abstract] |
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