  We present the first-principles determination of electronic stopping power
for protons and {\alpha} particles in a semiconductor material of great
technological interest: silicon carbide. The calculations are based on
nonequilibrium simulations of the electronic response to swift ions using
real-time, time-dependent density functional theory (RT-TDDFT). We compare the
results from this first-principles approach to those of the widely used linear
response formalism and determine the ion velocity regime within which linear
response treatments are appropriate. We also use the nonequilibrium electron
densities in our simulations to quantitatively address the longstanding
question of the velocity-dependent effective charge state of projectile ions in
a material, due to its importance in linear response theory. We further examine
the validity of the recently proposed centroid path approximation for reducing
the computational cost of acquiring stopping power curves from RT-TDDFT
simulations.
