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The Structure of Ideal Liquid Water


A Time-Averaged, Semi-Classical Model


Abstract

Ideal liquid water is here defined as a pure, (microcanonical) collection of water molecules in the liquid state without hydroxide or hydronium ions. This interstitial structure is described pictorially using geometry and mathematically using the thermodynamic partition function. The combined descriptions potentially make liquid water completely computerizeable. A semi-classical model is based on and is consistent with quantum mechanics but is described in classical terms.

After thoroughly examining the water molecule, a first approximation is made that the liquid structure is roughly the hexagonal cell structure of ice with the appropriate number of interstitial molecules needed to reproduce the observed density of a given temperature given the inter-molecular lengths seen by x-ray at that temperature.

Next a molecular stick-figure of these hexagonal cells is drawn with the interstitial molecules placed to minimize the inter-molecular electrical potential energy. The combined hexagonal and interstitial postitions are seen to reproduce the liquid x-ray data. The partition function, using the potential energies, translates the graphical picture into thermodynamic equations. These predict the observed entropy and other thermodynamic functions while explaining the abruptness of melting, the long transition of supercooling and other phenomena.

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