Molecular Dynamics Simulations of the Liquid/Vapor Interface of SPC/E Water

Abstract

Molecular dynamics computer simulations have been used to explore the structural and dynamical properties of water's liquid/vapor interface using the simple extended point charge (SPC/E) model. Comparisons to the existing experimental and simulation data suggest that the SPC/E potential energy function provides a semiquantitative description of this interface. The orientation of H2O molecules at the interface is found to be bimodal in nature. The self-diffusion constant of water is calculated to be larger at the surface than in the bulk.

Microscopic structure and dynamics of air/water interface by computer simulations—comparison with sum-frequency generation experiments

“…A more recent SFG experiment 14 yielded a similar average tilt angle, hy OH i E 301, with a narrow distribution width of r151, assuming a Gaussian distribution model. In contrast to these distributions and average orientations of free OH bonds, however, previous molecular dynamics simulations 3,[15][16][17][18]30 with various water models consistently predicted widths of the orientational distribution much broader than those assumed in the previous interpretations of SFG experiments. 1,9,14,29 We address this discrepancy by considering the nature of free OH bonds on the surface, and, in a procedure detailed below, selectively removing those that would likely not contribute to the SFG, allowing a direct comparison between our calculations and experimental measurements.…”

“…11 Roughly the same picture of the existence of the free OH bonds at the interface has since been consistently observed in SFG experiments by Richmond, 5 Eisenthal, 12 Allen, 13 and Gan et al, 14 and also in computer simulations. 3,[15][16][17][18][19] The structure of water at the hydrophobic organic/water interfaces was shown to be similar to that at the air/water interface. 9,20,21 In the process of understanding the air/water interface, different interpretations were also made in terms of details of the air/water interface using both experiments and computations.…”

Hydrogen-Bond Dynamics in the Air−Water Interface

“…Over the past two decades, considerable work has been done on the study of the hydrogen-bond behavior of water. [7][8][9][10][12][13][14][15][16] However, the previous studies have focused mainly on bulk water or solutes dissolved in bulk water. Some work has been done on hydrogenbond dynamics at vapor-liquid interfaces.…”

“…17 We expected to observe hydrogen-bond behavior similar to that found on the nonpolar surface of proteins 15,18 because the vapor phase is essentially nonpolar (low dielectirc constant) and the orientational distribution of water molecules next to hydrophobic surfaces is similar to that of water molecules in the liquid-vapor interface. 16,19 The formation and breaking of water-water hydrogen bonds are highly concerted processes, 18 and the relaxation rate of these processes increases as the number of adjacent but non-hydrogenbonded water molecules increases. Because the number of such "replacement" water molecules in the interfacial region is smaller than that in the bulk, one might expect the hydrogenbond dynamics to be slower.…”

Explosive Boiling of Water Films Adjacent to Heated Surfaces: A Microscopic Description

“…We believe that the model presented here provides the basis for understanding of the molecular-level processes leading to the separation of a H 2 O film from a heated substrate. many of the properties of bulk 16 H 2 O and the liquid/vapor interface 22 of H 2 O. In the SPC model, the molecular interaction potential U inter consists of an electrostatic component U electrostatic describing the charge-charge interaction between pairs of atoms in the two molecules.…”