Active Multi-Particle Collision Dynamics: Collision Operators for Coarse Grained Simulation of Active Nematic Liquid Crystals*

Coarse-grained simulations have proved to be an invaluable tool in the study of soft condensed matter due to their computational efficiency and their ability to model systems in which the background solvent plays a significant role but is not of principle interest. One successful method is Multi-Particle Collision Dynamics (MPCD), a mesoscopic particle-based algorithm that replaces pair interactions between fluid molecules with a many-particle stochastic collision operator, reproducing flows in long length-scales. MPCD algorithms have been extended to simulate complex fluids including nematic liquid crystals, and more. In this work, we present collision operators which extend MPCD to active systems. By including a novel activity term we obtain local dipole forces between fluid particles. Comparing to experimental flows in active nematic films, we conclude that our algorithm successfully captures key characteristics such as the continuous creation and annihilation of defect pairs and active turbulence. We expect that our extended MPCD will shed new light in the study of composite active-passive systems.