Theoretical characterization of the "ridge" in the supercritical region in the fluid phase diagram of water

Masaru Matsugami, Norio Yoshida, Fumio Hirata

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    Abstract

    The density fluctuation of water in the supercritical region was investigated theoretically using the reference interaction site model theory combined with the Kovalenko-Hirata closure relation, the so-called RISM-KH theory. The density fluctuation was evaluated by the numerical differentiation of density with respect to pressure at constant temperature. The density fluctuations plotted against density show finite maxima along a line slightly off from the critical isochore, in accordance with experimental results. The microscopic structures of water on both regions that were separated by the line were investigated by analyzing the site-site radial distribution functions. The analysis clearly indicates that the structure is determined by the two effects featuring liquid states: the packing or volume exclusion effect and the screening of the Coulomb interaction or the hydrogen bond, both becoming more important at higher densities. An interplay of the two effects creates maxima of the density fluctuation in the supercritical region of water.

    Original languageEnglish
    Article number104511
    JournalJournal of Chemical Physics
    Volume140
    Issue number10
    DOIs
    Publication statusPublished - Mar 14 2014

    All Science Journal Classification (ASJC) codes

    • Physics and Astronomy(all)
    • Physical and Theoretical Chemistry

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