Oscillatory surface tension due to finite-size effects

Abstract

The simulation results of surface tension at the liquid-vapor interface are presented for fluids interacting with Lennard Jones and square-well potentials. From the simulation of liquids we have reported [M. González-Melchor et al., J. Chem. Phys. 122, 4503 (2005)] that the components of pressure tensor in parallelepiped boxes are not the same when periodic boundary conditions and small transversal areas are used. This fact creates an artificial oscillatory stress anisotropy in the system with even negative values. By doing direct simulations of interfaces we show in this work that surface tension has also an oscillatory decay at small surface areas; this behavior is opposite to the monotonic decay reported previously for the Lennard Jones fluid. It is shown that for small surface areas, the surface tension of the square-well potential artificially takes negative values and even increases with temperature. The calculated surface tension using a direct simulation of interfaces might have two contributions: one from finite-size effects of interfacial areas due to box geometry and another from the interface. Thus, it is difficult to evaluate the true surface tension of an interface when small surface areas are used. Care has to be taken to use the direct simulation method of interfaces to evaluate the predicted surface tension as a function of interfacial area from capillary-wave theory. The oscillations of surface tension decay faster at temperatures close to the critical point. It is also discussed that a surface area does not show any important effect on coexisting densities, making this method reliable to calculate bulk coexisting properties using small systems.

Communication: Slab thickness dependence of the surface tension: Toward a criterion of liquid sheets stability

“…The first aim of this work is to show how the surface tension depends on thickness, and then to eventually extract a stability criterion from the microscopic study of the sheets. From a methodological viewpoint, it is well-known that the calculation of the surface tension of a two-phase system depends on a certain number of factors such as the finite size effects, [9][10][11][12] the range of interactions, [13][14][15][16] the truncation effects, 13,[17][18][19] the mechanical and thermodynamic definitions of the surface tension, 18,[20][21][22] and the long range corrections to the surface tension. 15,17,18,[22][23][24] This paper also contributes to this area of research by establishing the role of the slab thickness on the calculation of the surface tension of various systems interacting through different potential models.…”

A New Force Field of Formamide and the Effect of the Dielectric Constant on Miscibility

“…For the surface tension computations in the NVT ensemble the cutoff was set to 25Å, since the surface tension depends on the truncation of the interactions [25,17] and the interface cross sectional area [26,27]. The equilibration period for the interfacial simulations was 2 ns and the results for the average properties were obtained over an additional 6 ns trajectory.…”

Vapor–liquid surface tension of strong short-range Yukawa fluid

“…The new data reported with standard MC simulations were made using the same parameters as in previous works [13][14][15][16] , i. e., they were performed in a parallelepiped cell with sides L z = 40σ > L x = L y = 10σ and 1500 particles. It is well known that with these parameters finite size effects are avoided [46][47][48] . The new results were obtained with 6 × 10 7 MC steps to get more accurate values than in previous work 13 .…”