Abstract
Molecular dynamics simulations in a constant potential ensemble are an increasingly important tool to investigate charging mechanisms in next-generation energy storage devices. We present a highly efficient approach to compute electrostatic interactions in simulations employing a constant potential method (CPM) by introducing a particle-particle particle-mesh solver specifically designed for treating long-range interactions in a CPM. Moreover, we present evidence that a dipole correction term-commonly used in simulations with a slab-like geometry-must be used with caution if it is also to be used within a CPM. It is demonstrated that artifacts arising from the usage of the dipole correction term can be circumvented by enforcing a charge neutrality condition in the evaluation of the electrode charges at a given external potential.
Highlights
Molecular dynamics (MD) simulations are a popular method to investigate electrochemical processes of ionic liquids,1–4 supercapacitors,5–7 water in salt electrolytes,8,9 and batteries10,11 at the fundamental atomic level
There are already several constant potential method (CPM) implementations available, e.g., in the MetalWalls code27 or as an add-on for the molecular dynamics code Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS)28 by Wang et al.,17 we present here a new implementation of the CPM for LAMMPS that is conceptually more in line with the fundamental programming idea of LAMMPS by taking full advantage of its modularity
We demonstrated that the developed particle–particle particle–mesh (P3M) method facilitates the incorporation of long-range electrostatic interactions based on a constant potential approach at considerably smaller timescales in comparison to the previously employed techniques
Summary
Molecular dynamics (MD) simulations are a popular method to investigate electrochemical processes of ionic liquids, supercapacitors, water in salt electrolytes, and batteries at the fundamental atomic level For such cases, the constant potential method (CPM) has become a valuable tool in simulations involving an electrolyte between metallic electrodes. In contrast to the rather simple approach of using a homogeneous and constant charge on all electrode atoms, the CPM adjusts the charges of the electrode atoms as a function of a constant electric potential applied between the electrodes This method has been used to calculate the differential capacitance of various capacitor designs containing aqueous electrolytes or mixtures of ionic liquids and solvents as electrolytes.. The finite field method allows the use of a CPM with periodic boundary conditions in three dimensions for slabshaped geometries, requiring no artificial vacuum.24,25 Until now, these approaches only allow planar electrodes or a homogeneous distribution of charge. If the EW3Dc approach is used within the CPM, close attention should be paid to the charge neutrality, as will be demonstrated for a simple model capacitor containing an aqueous electrolyte between two metal electrodes
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