Finite field methods for the supercell modeling of charged insulator/electrolyte interfaces

Interactions between aligned dipoles in periodic model systems are often considered spurious and removed by partitioning the supercell in isolated slabs separated by vacuum layers. One popular and efficient screening approach is the so-called dipole correction. In this work, the authors present an alternative finite-field based method which retains all electrostatic interactions and dispenses with vacuum layers. Adapting the constant-D approach developed by Stengel, Spaldin, and Vanderbilt for the study of ferroelectric nanocapacitors, the new scheme here is intended for molecular dynamics simulations of the interface between an insulator carrying a specifically absorbed surface charge and an ionic conductor (the electrolyte) at finite temperature. The authors show that the dipole correction scheme is equivalent to D=0 electric boundary conditions with or without vacuum layers. Thus, both global polarization P of the heterogeneous system and corresponding average macroscopic electric field E are finite. The authors then continue with the investigation of the variation of P with E or D and validate expressions based on P for computing the electric double-layer capacitance using atomistic simulations.