The kink we found at \(v = 0.07~\mathrm{a.u.}\) can be explained by conservation laws in the effective homogeneous electron gas and general properties of electronic density of states in crystalline \(\mathrm{Cu}\). The minimum energy loss with maximum momentum transfer from an electron to an ion moving with velocity \(v\) are respectively \(2\hbar k_\text{F}v\) and \(2\hbar k_\text{F}\) (plus small corrections of order \(m_\text{e}/m_\text{p}\)). Due to Pauli exclusion, only electrons in the energy range \(E_\text{F} \pm 2\hbar k_\text{F} v\) can participate in the stopping process. Taking into account that DFT band structure predicts that the \(\mathrm{d}\)-band edge is \(\Delta_\text{DFT} = 1.6~\mathrm{eV}\) below the Fermi energy (see for example, Fig. 3(a) in Ref. \cite{Lin_2008}), that electron (band) effective mass close to \(1\) and that \(k_\text{F} = 0.72/a_0\) for the effective homogeneous electron gas of \(\mathrm{Cu}\) \(\mathrm{s}\)-electrons \cite{Ashcroft_2003}, we can derive an approximate value of \(v_\text{kink}\) caused by the participation of \(\mathrm{d}\)-electrons. Based in this DFT ground state density of states plus conservation laws, we obtain an estimate of \(v_\text{kink} = \Delta/(2\hbar k_\text{F}) = 0.41~\mathrm{a.u.}\) in near agreement with our TDDFT prediction. In reality, the \(\mathrm{d}\)-band is about \(\Delta_\text{exp} = 2~\mathrm{eV}\) below the Fermi energy as indicated by ARPES  \cite{Knapp_1979}, which means that both the DFT-based estimate and the full TDDFT result should be giving an underestimation of 25% of the kink location. The second (negative) kink at \(v = 0.3~\mathrm{a.u.}\) is more difficult to explain precisely as the qualitative description in terms of \(k_\text{F}\) (as in the homogeneous electron gas) becomes more ambiguous, but it is related to the point at which the whole conduction band (\(11\) ‘\(\mathrm{s} + \mathrm{d}\)’ electrons) starts participating in the process.