Long-range coulomb interaction for reactive atomistic simulations : application to graphene-water capacitors

Abstract

Electrochemical processes often govern contemporary energy storage and electronic devices. Despite the significant signs of progress achieved toward unveiling the properties of these devices, the mechanisms that control their operations are not fully understood, especially at the atomic level. Besides experiment limits, atomistic simulations can provide unprecedented insights and details about the processes and improve device development. Atomic description of these systems requires reactive interaction potential to be able to describe (i) the chemistry between atoms and those existing in molecules and (ii) the evolving charge distribution and polarization effects. Calculating Coulomb electrostatic interactions and polarization effects required a more accurate estimate of partial charge distribution in molecular systems, at least for the proper prediction of the stability and solubility of the system. To this purpose, the applications of many-body, partial bond-order potential alongside geometry-dependent partial atomic charge evaluation scheme led to the development of reactive force fields such as ReaxFF and the charge equilibration (QEq) models used in reactive molecular dynamics (MD) simulations. However, these models include Coulomb interactions up to only a short-range distance cut-off for better computational speeds, limiting the computation of Coulomb interaction up to a short distance around an atom. Ignoring long-range (LR)/distance electrostatic interaction affects the ability to describe electrochemistry in large systems. We emphasize evaluating and including long-range effects on partial charge and atom force calculations; and we investigate the long-range Coulomb effects among charged particles. By extending a QEq method to include long-range effects, we anticipated a proper account of Coulomb interactions in reactive molecular dynamics simulations. We validate the approach by computing charges on a series of metal-organic frameworks and some simple systems. Results are compared to regular QEq and quantum mechanics (QM) calculations. The study shows slightly overestimated charge values in regular QEq approach. Moreover, our method was combined with Ewald summation to compute forces and evaluate the long-range effects in simple capacitor configurations. There were noticeable differences between the calculated charges with/without long-range Coulomb interactions. The difference, which may have originated from the long-range influence on the capacitor ions, makes the Ewald method a better descriptor of Coulomb electrostatics for charged electrodes. The approach explored in this study enabled the atomic description of electrochemical systems with realistic electrolyte thickness while accounting for the electrostatic effects of charged electrodes throughout the dielectric layer in devices like batteries and emerging solid-state memory.