Charge fluctuations from molecular simulations in the constant-potential ensemble
Laura Scalfi1, David T Limmer2, Alessandro Coretti3
1Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France. benjamin.rotenberg@sorbonne-universite.fr.
Physical Chemistry Chemical Physics : PCCP
|January 8, 2020
Summary
This study clarifies charge fluctuations in capacitors, revealing a new contribution to differential capacitance from electrode charge dynamics. This effect is generally smaller than electrolyte-induced fluctuations.
Area of Science:
- Physical Chemistry
- Computational Electrochemistry
- Statistical Mechanics
Background:
- Capacitor charge fluctuations are crucial for understanding electrochemical energy storage.
- Constant-potential molecular simulations treat electrode atomic charges as dynamic variables.
- Electroneutrality and fixed potential constraints are key in these simulations.
Purpose of the Study:
- To derive a complete fluctuation-dissipation relation for differential capacitance.
- To elucidate the role of electroneutrality and Born-Oppenheimer averages.
- To quantify the contribution of electrode charge fluctuations to capacitance.
Main Methods:
- Classical molecular simulations under constant-potential conditions.
- Analysis of statistical mechanics for charge fluctuations.
- Derivation of fluctuation-dissipation relations.
Main Results:
- A complete fluctuation-dissipation relation for differential capacitance is derived.
- A novel contribution from electrode charge fluctuations is identified.
- This contribution is shown to be small compared to electrolyte effects for typical liquids.
Conclusions:
- Electrode charge fluctuations contribute to differential capacitance even without an electrolyte.
- The derived relation provides a more comprehensive understanding of capacitor behavior.
- Numerical validation confirms theoretical predictions for various electrode-electrolyte systems.
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