where z w is the wall position, ε w describes the strength of the wall-particle interaction, and z is the vertical position of the centre of the fluid particle. This repulsive wall was implemented at the top surface of the fluid to maintain an approximately constant average fluid density between systems with particles of the same shape and to prevent evaporation. Similar to a vapour interface, this wall constrained only the vertical position of the centre of a fluid particle and placed no constraints on the position of the particle surface defined by the repulsive part of the GB potential.