Abstract
The liquid-vapor equilibrium isotopic fractionation of water is determined
by molecular-based simulation, via Gibbs Ensemble Monte Carlo and
isothermal-isochoric molecular dynamics involving two radically different
but realistic models, the extended simple point charge (SPC/E) and the
Gaussian charge polarizable (GCP) models. The predicted temperature
dependence of the liquid-vapor equilibrium isotopic fractionation factors
for H
2
18O / H
2
16O, H
2
17O / H
2
16O, and 2H 1H 16O / 1H
2
16O are compared
against the most accurate experimental datasets to assess the ability of
these intermolecular potential models to describe quantum effects
according to the Kirkwood-Wigner free energy perturbation
!
2
!expansion. Predictions of the vapor pressure isotopic effect for the
H
2
18O / H
2
16O and H
2
17O / H
2
16O pairs are also presented in comparison
with experimental data and two recently proposed thermodynamic
modeling approaches. Finally, the simulation results are used to discuss
some approximations behind the microscopic interpretation of isotopic
fractionation based on the underlying roto-translational coupling.