Relating the steady states of 3D dry active nematics to microscopic parameters through particle-based simulations

Active nematic liquid crystals exhibit a wide range of fascinating topological structures and dynamics, many of which are forbidden in equilibrium systems. Although it is well known that such systems form complex defect networks in 3D [1-4], the relationship between a system’s microscopic parameters and its coarse-grained macroscopic properties is unclear. In this work, we perform large-scale particle-based simulations of 3D dry active nematic filaments to understand the connection between microscopic simulation parameters, such as the bending stiffness and active force amplitude, and the emergent coarse-grained parameters. We find that the collective behaviors of this nonequilibrium system can be described by coarse-grained moduli analogous to an equilibrium system, but that activity significantly renormalizes the apparent material constants. The relative values of these effective moduli reflect the fact that the particle-scale energy injected by activity dissipates preferentially into certain modes. For example, the coarse-grained effective bending modulus can be understood to arise from a balance between the filaments’ intrinsic bending stiffness and activity-induced collisions.