We report the nearest-neighbor oxygen-oxygen radial distribution function (NN O-O RDF) of room temperature liquid water and polycrystalline ice Ih (-16.8 degrees C) obtained by x-ray Raman based extended x-ray absorpt...
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We report the nearest-neighbor oxygen-oxygen radial distribution function (NN O-O RDF) of room temperature liquid water and polycrystalline ice Ih (-16.8 degrees C) obtained by x-ray Raman based extended x-ray absorption fine structure (EXAFS) spectroscopy. The spectra of the two systems were taken under identical experimental conditions using the same procedures to obtain the NN O-O RDFs. This protocol ensured a measurement of the relative distance distribution with very small systematic errors. The NN O-O RDF of water is found to be more asymmetric (tail extending to longer distances) with longer average distance (2.81 angstrom for water and 2.76 angstrom for ice) but a slightly shorter peak position (2.70 angstrom for water and 2.71 angstrom for ice). The refinement also showed a small but significant contribution from the linear O-H-O multiple scattering signal. The high sensitivity to short range distances of the EXAFS probe will set further restrictions to the range of possible models of liquid water. (c) 2007 American Institute of Physics.
It is well known that the exchange - correlation ( XC) potential at a metal surface has an image- like asymptotic behaviour given by - 1/4( z - z(0)), where z is the coordinate perpendicular to the surface. Using a su...
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It is well known that the exchange - correlation ( XC) potential at a metal surface has an image- like asymptotic behaviour given by - 1/4( z - z(0)), where z is the coordinate perpendicular to the surface. Using a suitable fully non- local functional prescription, we evaluate self- consistently the XC potential with the correct image behaviour for simple jellium surfaces in the range of metallic densities. This allows a proper comparison between the corresponding imageplane position, z(0), and other related quantities such as the centroid of an induced charge by an external perturbation. As a by- product, we assess the routinely used local density approximation when evaluating electron density profiles, work functions, and surface energies by focusing on the XC effects included in the fully non- local description.
Due to its ubiquity in our environment (near or far remote) water is the most investigated liquid of the literature. Since the advent of molecular simulations in the sixties the key point of the theoretical studies on...
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Due to its ubiquity in our environment (near or far remote) water is the most investigated liquid of the literature. Since the advent of molecular simulations in the sixties the key point of the theoretical studies on water is the description of its force field. During the last three decades a cohort of model potentials have been published and tested by computer simulations. Our purpose is to appraise what have been accomplished during all these years and what deserves to be improved. In addition we attempt to give some guidance for future investigations. (C) 2002 Elsevier Science B.V. All rights reserved.
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