  The collective behavior of active semiflexible filaments is studied with a
model of tangentially driven self-propelled worm-like chains. The combination
of excluded-volume interactions and self-propulsion leads to several distinct
dynamic phases as a function of bending rigidity, activity, and aspect ratio of
individual filaments. We consider first the case of intermediate filament
density. For high-aspect-ratio filaments, we identify a transition with
increasing propulsion from a state of free-swimming filaments to a state of
spiraled filaments with nearly frozen translational motion. For lower aspect
ratios, this gas-of-spirals phase is suppressed with growing density due to
filament collisions; instead, filaments form clusters similar to self-propelled
rods, as activity increases. Finite bending rigidity strongly effects the
dynamics and phase behavior. Flexible filaments form small and transient
clusters, while stiffer filaments organize into giant clusters, similarly as
self-propelled rods, but with a reentrant phase behavior from giant to smaller
clusters as activity becomes large enough to bend the filaments. For high
filament densities, we identify a nearly frozen jamming state at low
activities, a nematic laning state at intermediate activities, and an
active-turbulence state at high activities. The latter state is characterized
by a power-law decay of the energy spectrum as a function of wave number. The
resulting phase diagrams encapsulate tunable non-equilibrium steady states that
can be used in the organization of living matter.
