Vapor-liquid equilibria from the triple point up to the critical point for the
new generation of TIP4P like models: TIP4P/Ew, TIP4P/2005 and TIP4P/Ice
C. Vega, J.L.F. Abascal and I. Nezbeda
Journal of Chemical Physics 125, 034503 (2006)
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[DOI]
ABSTRACT
The vapor liquid equilibria of three recently proposed water models
has been computed using Gibbs Duhem simulations. These models are
TIP4P/Ew, TIP4P/2005 and TIP4P/Ice and can be considered as modified
versions of the TIP4P model. By design TIP4P reproduces the
vaporization enthalpy of water at room temperature, whereas TIP4P/Ew
and TIP4P/2005 match the temperature of maximum density and
TIP4P/Ice the melting temperature of water. Recently the melting
point for each of these models has been computed, making it possible
for the first time to compute the complete vapor-liquid equilibria
curve from the triple point to the critical point. From the
coexistence results at high temperature, it is possible to estimate
the critical properties of these models. None of them is
capable of reproducing accurately the critical pressure or the vapor
pressures and densities. Additionally, in the cases of TIP4P and
TIP4P/Ice the critical temperatures are too low and too high
respectively compared to the experimental value. However, models
accounting for the density maximum of water, such as TIP4P/Ew and
TIP4P/2005, provide a better estimate of the critical temperature.
In particular TIP4P/2005 provides a critical temperature just 7~K
below the experimental result as well as an extraordinarily good
description of the liquid densities from the triple point to the
critical point. All TIP4P like models present a ratio of the triple
point temperature to the critical point temperature of about 0.39,
compared with the experimental value of 0.42. As is the case for any
effective potential neglecting many body forces, TIP4P/2005 fails in
describing simultaneously the vapor and the liquid phase of water.
However it can be considered as one of the best effective potentials
of water for describing condensed phases, both liquid and solid. In
fact it provides a completely coherent view of the phase diagram of
water including fluid-solid, solid-solid and vapor-liquid
equilibria.
