Molecular Modeling of Water Interfaces: From Molecular Spectroscopy to Thermodynamics

Abstract

Understanding aqueous interfaces at the molecular level is not only fundamentally important, but also highly relevant for a variety of disciplines. For instance, electrode-water interfaces are relevant for electrochemistry, as are mineral-water interfaces for geochemistry and air-water interfaces for environmental chemistry; water-lipid interfaces constitute the boundaries of the cell membrane, and are thus relevant for biochemistry. One of the major challenges in these fields is to link macroscopic properties such as interfacial reactivity, solubility, and permeability as well as macroscopic thermodynamic and spectroscopic observables to the structure, structural changes, and dynamics of molecules at these interfaces. Simulations, by themselves, or in conjunction with appropriate experiments, can provide such molecular-level insights into aqueous interfaces. In this contribution, we review the current state-of-the-art of three levels of molecular dynamics (MD) simulation: ab initio, force field, and coarse-grained. We discuss the advantages, the potential, and the limitations of each approach for studying aqueous interfaces, by assessing computations of the sum-frequency generation spectra and surface tension. The comparison of experimental and simulation data provides information on the challenges of future MD simulations, such as improving the force field models and the van der Waals corrections in ab initio MD simulations. Once good agreement between experimental observables and simulation can be established, the simulation can be used to provide insights into the processes at a level of detail that is generally inaccessible to experiments. As an example we discuss the mechanism of the evaporation of water. We finish by presenting an outlook outlining four future challenges for molecular dynamics simulations of aqueous interfacial systems.

Surface Structure of Organic Carbonate Liquids Investigated by Molecular Dynamics Simulation and Sum Frequency Generation Spectroscopy

“…We also note in passing that the surface tension is rather insensitive to the details of the short-range electrostatic interaction. 65 As shown in Table 4, the calculated results show reasonable agreement with experimental values. [66][67][68][69][70] We also find that the calculated results of density, heat of vaporization and surface tension are slightly overestimated for both PC and DMC.…”

Solvation Dynamics of CO2(g) by Monoethanolamine at the Gas–Liquid Interface: A Molecular Mechanics Approach

“…Notably, Du et al measured the surface vibrational spectrum by using the sum frequency generation technique to address the hydrophobicity of the air–water interface and identified the spectroscopic fingerprint of the dangling hydroxyl groups [ 26 ]. Electrostatic interactions resulting from such dangling hydroxyl groups at the air–water interface favored the solvation of anionic ions, as previously reported [ 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. Thus, the solvation phenomena of nonpolar CO 2 molecules containing the quadruple moment at the air–alcoholamine interface inspired the present study.…”

Ion Exclusion at the Ice-Water Interface Differs from That at the Hydrate-Water Interface: Consequences for Methane Hydrate Exploration

“…Our results will be useful for the confirmation of molecular models of the ice/water interface, such as the recent work of Nagata et al [14]. Next steps might now be to look at other hydrate formers at one atmosphere such as cyclopentane and then to move to high pressure systems such as methane.…”