(Received: September 11, 2008; Accepted for publication: November 7, 2008; Advance publication: December 22, 2008)
The Gibbs free energies of proton-ordered ices were estimated by molecular dynamics simulations. The ordered structures were obtained using NTV ensemble molecular dynamics of cells with small numbers of molecules, where the cut off distance for short range interaction was 1.4×10-9 m. The internal energy and volume were obtained by NTp molecular dynamics simulations at T = 1 K for each type of ice, where the cut off distance for short range interaction was half of the unit cell and the Ewald method was used to determine coulombic interaction. The infinite number limits in the internal energies of each ice type at T = 1 K were estimated. The enthalpy temperature dependence was calculated and the low temperature limit was estimated to obtain the Gibbs free energy at low temperatures. Phase transition pressures obtained were satisfactory when compared with the experimental results, at least qualitatively.
$B%-!<%o!<%I(B: Proton-ordered ices, Molecular dynamics, Gibbs free energies, Phase transition pressures
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