Molecular dynamics study of water clusters, liquid, and liquid–vapor interface of water with many-body potentials

Abstract

The molecular dynamics computer simulation technique is used to develop a rigid, four-site polarizable model for water. The suggested model reasonably describes the important properties of water clusters, the thermodynamic and structural properties of the liquid and the liquid/vapor interface of water. The minimum energy configurations and the binding energies for these clusters are in reasonable agreement with accurate electronic structure calculations. The model predicts that the water trimer, tetramer, and pentamer have cyclic planar minimum energy structures. A prismlike structure is predicted to be lowest in energy for the water hexamer, and a cagelike structure is the second lowest in energy, with an energy of about 0.2 kcal/mol higher than the prismlike structure. The results are consistent with recent quantum Monte Carlo simulations as well as electronic structure calculations. The computed thermodynamic properties for the model, at room temperature, including the liquid density, the enthalpy of vaporization, as well as the diffusion coefficient, are in excellent agreement with experimental values. Structural properties of liquid water, such as the radial distribution functions, neutron, and x-ray scattering intensities, were calculated and critically evaluated against the experimental measurements. In all cases, we found the agreement between the observed data and the computed properties to be quite reasonable. The computed density profile of the water's liquid/vapor interface shows that the interface is not sharp at a microscopic level and has a thickness of 3.2 Å at 298 K. These results are consistent with those reported in earlier work on the same systems. The calculated surface tension at room temperature is in reasonable agreement with the corresponding experimental data. As expected, the computed average dipole moments of water molecules near the interface are close to their gas phase values, while water molecules far from the interface have dipole moments corresponding to their bulk values.

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.…”

Molecular Dynamics Simulations of Water with Novel Shell-Model Potentials

“…We have only included potentials for which liquid simulation data were available. Results for the models TIP4P-FQ, 22 Dang,20 RER(pol), 17 PPC, 19 SPC-pol-1 and TIP4P-pol-3, 21 and MCDHO 64 have been added to Tables 5-7. 3.8.1. Liquid.…”

“…Subsequently, other models were proposed on the the basis of the same principles of three charged sites and a point polarizability. [14][15][16][17][18][19][20][21] These models are a genuine improvement on the older models because the Lennard-Jones parameters as well as the charges have been optimized to reproduce critical observables.…”

A transferable H2O interaction potential based on a single center multipole expansion: SCME

“…A common feature of these potentials is enhanced multipole moments of the molecules representing the effects of the mean-field, many-body polarization seen in the liquid and the solid. Although this approach gives reasonable results for several properties of the bulk phase, it has been shown that the explicit introduction of manybody polarization effects is required to accurately describe other environments, for example water clusters [51,52,53,54]. Pedulla and Jordan [51] have shown that nonadditive interactions play an important role in the description of phase changes in small clusters, an observation that is likely to extend to processes such as premelting, island formation on surfaces and diffusion.…”