A computer simulation study of the liquid–vapor coexistence curve of water

Abstract

The liquid–vapor coexistence curve of a model water (the extended simple point charge model, SPCE) is evaluated by molecular dynamics simulation in the (N,V,E) ensemble. It is shown that the simulated system (N=256 water molecules) is too small to present a spinodal decomposition and, hence, can be described by a classical equation of state whose the critical parameters (Tc=651.7 K, ρc=0.326 g/cm3, and Pc=189 bar) are found to be very close to that of real water (Tc=647.13 K, ρc=0.322 g/cm3, and Pc=220.55 bar). The critical parameters for SPCE water in the thermodynamic limit are deduced from the simulation data employing Wegner type expansions for the order parameter and the coexistence curve diameter; here also the values of the critical parameters (Tc=640 K, ρc=0.29 g/cm3, and Pc=160 bar) are close to that of real water. The temperature dependence of the dielectric constant for water and steam at orthobaric densities is next evaluated between ambient and Tc; the agreement with the experimental data is quite remarkable (e.g., εSPCE=81.0 at 300 K and εSPCE=6. at Tc instead of 78.0 and 5.3, respectively, in real water). The modifications experienced by water’s architecture with the temperature are deduced from the evaluation of the atom–atom correlation functions. It is shown that a structural change occurs in the temperature range 423–473 K. This important reorganization is characterized by a shift of the second shell of neighbors from 4.5 to 5.5 A and the loss of almost all angular correlations beyond the first solvation shell. Moreover, it is observed that the average number of hydrogen bonds per molecule nHB scales with the density all along the saturation curve. In the same way the values of nHB for orthobaric densities seems to follow a law analogous to the law of rectilinear diameter for orthobaric densities.

Structural, vibrational, and thermal properties of densified silicates: Insights from molecular dynamics

“…The following range has been studied : 1.5 ̺ 5.5 g/cm 3 and 1500 T 3000 K, which correspond to the following pressure range : −2.23 P 150 GPa. In contrast with previous works on molecular fluids 84,85 and silica, where the data were fitted using a Van der Waals type EOS, the data of the current simulations were fitted with a Birch-Murnaghan equation of state (BM EOS) that has a simpler form 86,87 . It has revealed to give reasonable fits in the case of a liquid densified germania 88 and is widely used in geophysical studies (see for example 89 ).…”

The liquid-vapor equilibria of TIP4P/2005 and BLYPSP-4F water models determined through direct simulations of the liquid-vapor interface

“…27,28 Application of this procedure requires the measurement of ρ l and ρ g . This is frequently accomplished by fitting the density distribution across the interface using a profile function.…”

The isotropic nuclear magnetic shielding constants of acetone in supercritical water: A sequential Monte Carlo/quantum mechanics study including solute polarization

“…As our major interest here is the description of the magnetic properties of the solute in SCW condition, we have decided for the extended simple point charge 51 ͑SPC/E͒ model because it leads to a very good agreement with experiment for the critical point of water. 52,53 For the acetone, we used the Lennard-Jones parameters of Gao 35 and the atomic charges were obtained using an electrostatic potential fit ͑CHELPG͒ 54 from a HF/ 6-311 + +G͑d , p͒ calculation, 55 as suggested. 56 Hence, we shall term this as the unpolarized model of the solute.…”