Spontaneous velocity alignment of active particles with rotational inertia

In the overdamped active Brownian particle system, spontaneous velocity alignment is likely to occur. For larger active particles, the effects of inertia are indispensable. However, the impact of rotational inertia on the spontaneous alignment velocity remains unclear. To answer this question, we study the spontaneous velocity alignment within an active particles system characterized by rotational inertia and pure repulsive interactions. We found that the self-propulsion speed, the rotational diffusion coefficient, and the rotational inertia significantly influence the extent of global velocity alignment. An increase in the self-propulsion speed induces a transition of the system from solid-like to liquid-like states, leading to an initial decrease followed by an increase in the degree of velocity alignment. A decrease in the rotational diffusion coefficient or an increase in the rotational inertia can facilitate the emergence of spontaneous global velocity alignment because of an increase in the effective persistence time. When the rotational inertia is exceedingly large, the system even exhibits spontaneous global velocity alignment. Nevertheless, in the critical state between solid-like state and liquid-like state, both decreasing the rotational diffusion coefficient and increasing the rotational inertia can hinder global velocity alignment by driving the system to a critical state with higher fluidity. © 2024 Elsevier B.V.