Importantly, the surface energy thus computed can be positive or negative. The reason is that there does not have to be a diminishment in P xx = P zz at the wall. In fact, the particle density profile can show an excess, for example for a pure hard wall without any additional During the simulation we measure the pressure tensor every 50 timesteps, obtained as output of dl meso, and incorporating the contribution of the wall forces as described in the Appendix. This is the default position in dl meso 2.8 onwards but not for earlier versions of the package.