where z i is the height of the i-th particle above the hard reflecting boundary at z = 0. We set the wall potential to have the same functional form for all bead types, but differentiate these from each other by bead-specific repulsion amplitudes A s,i , intended to capture the surface chemistry. For simplicity we set the range here equal to unity (in units of r c ) for all bead types though one could envisage this being used as an additional fine-tuning parameter.