  Electronic stopping power in the \(\mathrm{keV/\AA}\) range is accurately
calculated from first principles. The energy loss to electrons in
self-irradiated nickel, a paradigmatic transition metal, using real-time
time-dependent density functional theory is studied. Different core states are
explicitly included in the simulations to understand their involvement in the
dissipation mechanism. The experimental data are well reproduced in the
projectile velocity range of \(1.0 - 12.0~\mathrm{atomic~units}\). The core
electrons of the projectile are found to open additional dissipation channels
as the projectile velocity increases. Almost all of the energy loss is
accounted for, even for high projectile velocities, when core electrons as deep
as \(2s\) are explicitly treated. In addition to their expected excitation at
high velocities, a flapping dynamical response of the core electrons is
observed at intermediate projectile speeds.
