  In non-equilibrium molecular dynamics simulations of dense athermal shear
flows, we observe the transition from shear thinning to shear thickening at a
crossover shear rate $\dot\gamma_c$. Shear thickening occurs when $\frac{{\rm d
(ln} T_g)}{{\rm d (ln}\dot\gamma)}>2$ with $T_g$ the granular temperature. At
the transition, the pair distribution function shows the strongest anisotropy.
Meanwhile, the dynamics undergo apparent changes, signified by distinct scaling
behaviors of the mean squared displacement and relaxation time on both sides of
$\dot\gamma_c$. These features serve as robust signatures of the shear
thinning-thickening transition.
