Evaluation of the constant potential method in simulating electric double-layer capacitors

Wang, Zhenxing; Yang, Yongqiang; Olmsted, David L.; Asta, Mark; Laird, Brian B.

doi:10.1063/1.4899176

Cited by 196 publications

(226 citation statements)

References 46 publications

(53 reference statements)

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“…Under such constraint condition, the electric potential Ψ i on each electrode atom is constant over entire electrode, and is equal to the preset applied external potential Ψ , Ψ = Ψ i = ə U /ə q i , where i is the electrode atom index and U is the Coulomb energy of the whole system. The practical implementation of the CPM involves a replacement of the electrode point charge with a Gaussian charge distribution, in order to ensure the system of the linear equations relating q i shown above has a solution.…”

Section: Methodsmentioning

confidence: 99%

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

Yang

Wang²,

Liang

et al. 2019

Chin. J. Chem.

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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.

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Section: Methodsmentioning

confidence: 99%

“…All the MD simulations in this work are performed using CPM incorporated LAMMPS program . The SHAKE algorithm is used to hold bonds and angles (in water molecule) rigid at every MD step .…”

Section: Methodsmentioning

confidence: 99%

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

Yang

Wang²,

Liang

et al. 2019

Chin. J. Chem.

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“…In order to take into account the electrode polarization, we employ the constant potential method in this work. In the method, unlike conventional MD simulation methods with a fixed charge on each electrode atom, the charges on the electrode atoms change at each time step of a simulation depending on the motions of electrolyte molecules.…”

Section: Methodsmentioning

confidence: 99%

“…Although many classical MD simulations have been performed in the constant (or fixed) charge framework, they do not take into account such electrostatic interaction. In the present study, we treat the electrode polarization by using a constant potential method which allows the electrode atomic charges to fluctuate in response to the local interfacial electrolyte structure . In addition, the method has another advantage of being able to impose a desired potential difference between the electrodes because it is based on the requirement that the potential on the electrode atoms is kept to a specified value.…”

Section: Introductionmentioning

confidence: 99%

Electrode polarization effects on interfacial kinetics of ionic liquid at graphite surface: An extended lagrangian‐based constant potential molecular dynamics simulation study

Inagaki

Nagaoka

2019

J Comput Chem

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Computational models including electrode polarization can be essential to study electrode/electrolyte interfacial phenomena more realistically. We present here a constant‐potential classical molecular dynamics simulation method based on the extended Lagrangian formulation where the fluctuating electrode atomic charges are treated as independent dynamical variables. The method is applied to a graphite/ionic liquid system for the validation and the interfacial kinetics study. While the correct adiabatic dynamics is achieved with a sufficiently small fictitious mass of charge, static properties have been shown to be almost insensitive to the fictitious mass. As for the kinetics study, electrical double layer (EDL) relaxation and ion desorption from the electrode surface are considered. We found that the polarization slows EDL relaxation greatly whereas it has little impact on the ion desorption kinetics. The findings suggest that the polarization is essential to estimate the kinetics in nonequilibrium processes, not in equilibrium. © 2019 Wiley Periodicals, Inc.

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“…It may also be required to further calculate electron transfer processes between the electrode and electrolyte (Petersen et al, 2012). Several methods have been trialed in the literature to model electrodes (Siepmann and Sprik, 1995;Straus et al, 1995;Calhoun and Voth, 1996;Crozier et al, 2000;Lanning and Madden, 2004;Fedorov and Kornyshev, 2008;Lamperski and Kłos, 2008;Wang et al, 2014). Initial attempts included assigning the individual electrode atoms with fixed partial charges, which summed up to equal to the total electrode charge (this was know as the constant charge approach) (Lanning and Madden, 2004).…”

Section: Introductionmentioning

confidence: 99%

Modeling Electric Double-Layer Capacitors Using Charge Variation Methodology in Gibbs Ensemble

Pavaskar

Ramakrishnasubramanian

Kandagal

et al. 2018

Front. Energy Res.

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Supercapacitors deliver higher power than batteries and find applications in grid integration and electric vehicles. Recent work by Chmiola et al. (2006) has revealed unexpected increase in the capacitance of porous carbon electrodes using ionic liquids as electrolytes. The work has generated curiosity among both experimentalists and theoreticians. Here, we have performed molecular simulations using a recently developed technique (Punnathanam, 2014) for simulating supercapacitor system. In this technique, the two electrodes (containing electrolyte in slit pore) are simulated in two different boxes using the Gibbs ensemble methodology. This reduces the number of particles required and interfacial interactions, which helps in reducing computational load. The method simulates an electric double-layer capacitor (EDLC) with macroscopic electrodes with much smaller system sizes. In addition, the charges on individual electrode atoms are allowed to vary in response to movement of electrolyte ions (i.e., electrode is polarizable) while ensuring these atoms are at the same electric potential. We also present the application of our technique on EDLCs with the electrodes modeled as slit pores and as complex three-dimensional pore networks for different electrolyte geometries. The smallest pore geometry showed an increase in capacitance toward the potential of 0 charge. This is in agreement with the new understanding of the electrical double layer in regions of dense ionic packing, as noted by Kornyshev's theoretical model (Kornyshev, 2007), which also showed a similar trend. This is not addressed by the classical Gouy-Chapman theory for the electric double layer. Furthermore, the electrode polarizability simulated in the model improved the accuracy of the calculated capacitance. However, its addition did not significantly alter the capacitance values in the voltage range considered.

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Evaluation of the constant potential method in simulating electric double-layer capacitors

Cited by 196 publications

References 46 publications

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

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

Electrode polarization effects on interfacial kinetics of ionic liquid at graphite surface: An extended lagrangian‐based constant potential molecular dynamics simulation study

Modeling Electric Double-Layer Capacitors Using Charge Variation Methodology in Gibbs Ensemble

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