  We have investigated the onset of collective motion in systems of model
microswimmers, by performing a comprehensive analysis of the binary collision
dynamics using three dimensional direct numerical simulations (DNS) with fully
resolved hydrodynamics. From this data, we have constructed a simplified binary
collision model (BCM) which accurately reproduces the collective behavior
obtained from the DNS for most cases. Thus, we show that global alignment can
mostly arise solely from binary collisions. Although the agreement between both
models (DNS and BCM) is not perfect, the parameter range in which notable
differences appear is also that for which strong density fluctuations are
present in the system (where pseudo-sound mound can be observed[1]).
