Capillary waves at the liquid-vapor interface and the surface tension of water models.pdf
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Capillary waves at the liquid-vapor interface and the surface tension of water models
Ahmed E. Ismail, Gary S. Grest, and Mark J. Stevens
Sandia National Laboratories, Albuquerque, NM 87185
(Dated: February 6, 2008)
Capillary waves occurring at the liquid-vapor interface of water are studied using molecular dy-
namics simulations. In addition, the surface tension, determined thermodynamically from the differ-
ence in the normal and tangential pressure at the liquid-vapor interface, is compared for a number
of standard three- and four-point water models. We study four three-point models (SPC/E, TIP3P,
TIP3P-CHARMM, and TIP3P-Ew) and two four-point models (TIP4P and TIP4P-Ew). All of the
models examined underestimate the surface tension; the TIP4P-Ew model comes closest to repro-
ducing the experimental data. The surface tension can also be determined from the amplitude of
capillary waves at the liquid-vapor interface by varying the surface area of the interface. The sur-
face tensions determined from the amplitude of the logarithmic divergence of the capillary interfacial
width and from the traditional thermodynamic method agree only if the density profile is fitted to
an error function instead of a hyperbolic tangent function.
I. INTRODUCTION
The ability to derive accurate property predictions for
the liquid-vapor interface is a key test for an atomistic
force field. Because of the frequent occurrence of water
in systems of chemical and biological interest, interfacial
property prediction is especially vital for force fields of
water. The most important of these properties is surface
tension, an intensive quantity that measures the differen-
tial surface work required to increase the interfacial area.
Accurate models of the surface tension of water are essen-
tial for conducting large-scale simulations of the wetting
and spreading of water droplets at surface
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