Thank you for your reply. I have seen this paper earlier. However, I still exactly dont understand the mechanism used in Espresso for the swimming feature, that how this orientation (u) is updated. Does it follow a separate equation of motion like a Langevin equation for rotation, which gets updated at each step along with position and then the force (F) is applied in that direction? Otherwise it is difficult for Espresso to find the orientation of a symmetric single particle. I am trying to understand for a system without any Hydrodynamic interaction.