A Constant Potential Molecular Dynamics Simulation Study of the Atomic‐Scale Structure of Water Surfaces Near Electrodes

Abstract

Summary of main observation and conclusion Novel and technologically important processes and phenomena arise at water surfaces in the presence of electric fields. However, experimental measurements on water surfaces are challenging, and the results are scarce and inconclusive. In this work, the constant potential molecular dynamics method, in which the electrode charges are allowed to fluctuate to keep the electric potential fixed, was implemented in the study of a near‐electrode water surface systems. This simulation system was set up with a vapor/liquid‐water/vapor slab and two electrodes under different sets of applied electrostatic potential, yielding i) a detailed characterization of the external E‐field dependent electrostatic potential/density/dipole moment density profiles, and ii) the relationship between the water surface width and the applied electrode voltage differences which has been rarely reported. The adjustments in the number density profiles in the vicinity of water surfaces due to external E‐fields were observed, while the capillary interfacial widths for the surfaces near both cathode and anode were found with different increment rates under increasing E‐fields. By examining dipole density profiles across the water surfaces, we found that external E‐field induced polarization occurs in both bulk and surface regimes, yet the surface polarization densities vary asymmetrically with respect to the increasing E‐fields. Detailed discussions were carried out to explain the correlation between water surface tension and surface widths, as well as the interplay between the surface polarization densities and the hydrogen bond network structure. We conclude that the mechanical and structural properties of the water surfaces could be tuned by both magnitude and direction of the strong external E‐fields. We also recognize that more surface properties with application value, such as dielectric permittivity tensor or surface potential, could also be regulated by the external E‐fields.

An evaluation of the capacitive behavior of supercapacitors as a function of the radius of cations using simulations with a constant potential method

“…3a, as a result of decreasing the bulk concentration of ions and consequently increasing the surface charge. We must stress that, although a similar oscillatory potential pattern was described in the literature, 21,24,25,27,28,43,45 to the best of our knowledge, it is the first study concerning the monocation sulfate electrolyte for two different voltages.…”

“…The charges on each electrode atom are altered to constrain constant potential in the electrode at every step. As a result, the electric potential is equal to the applied external potential 45 along the whole electrode surface.…”

Atomistic Insights into Oxidation of Chemical Passivated Silicon (100) Surface: Reactive Molecular Dynamic Simulations

“…At present, molecular simulation is becoming the favorite tool to investigate the surface process, [ 55,61 ] especially, the ReaxFF interatomic potential simulations are used to explore the interface oxidation mechanisms of the Si surface. [ 39‐40 ] Compared with Si (111) surface, the Si (100) surface is easier to be oxidized due to the lower index surface.…”

The nonlocal dielectric response of water in nanoconfinement

“…In MD simulations, the position of the interfaces is not as clear-cut as in theory due to thermal capillary fluctuations and the non-infinitly sharp repulsion of the surfacefluid LJ interaction. [35] This is taken into account by applying a smearing to the theoretical predictions, gen density peak with a Gaussian G(z) which position and width define z 0 and η (see SM for details). The hBN surface is characterized by a deeper LJ potential and consequently a smaller dispersion η than the graphene.…”