  We present real-time time-dependent density-functional-theory calculations of
the electronic stopping power for negative and positive projectiles (electrons,
protons, antiprotons and muons) moving through liquid water. After correction
for finite mass effects, the nonlinear stopping power obtained in this work is
significantly different from the previously known results from semi-empirical
calculations based on the dielectric response formalism. Linear-nonlinear
discrepancies are found both in the maximum value of the stopping power and the
Bragg peak's position. Our results indicate the importance of the nonlinear
description of electronic processes, particularly for electron projectiles,
which are modeled here as classical point charges. Our findings also confirm
the expectation that the quantum nature of the electron projectile should
substantially influence the stopping power around the Bragg peak and below.
