Molecular dynamics (MD) calculation of the zeta potential of neutral surfaces

Abstract

Molecular dynamics (MD) simulations of the zeta potential are so poor that it has become common to term their predictions 'apparent'. Here we demonstrate how zeta potentials that agree with measured values can be calculated by: (1) integrating the net average charge in surface-parallel layers from the midpoint of the fluid layer (where the electrostatic potential is zero) to and then into two solid caps, (2) determining the position of slipping plane with separate Couette flow models, and (3) calculating the charge distribution and electrostatic potential under static conditions. The solids we model are charge neutral surfaces composed of atoms with zero charge or charge balanced monovalent or divalent ions. The zeta potentials calculated are within a few millivolts of measured values, and the measured values fall within the simulation error bars. Insights provided by the improved MD simulations into the complex phenomena that affect surface charge and zeta potential are discussed.