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that electron (band) effective mass are close to $1$ for and $k_\text{F} = 0.72$ for $\mathrm{Cu}$ $\mathrm{s}$-electrons \cite{Ashcroft_2003}.   Based in this DFT ground state density of states plus conservation laws we obtain an estimate of $v_\text{kink} = \Delta/\hbar/k_\text{F} = 0.082~\mathrm{a.u.}$ in qualitative agreement with the 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}, that means that both the DFT-based estimate and the 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 $k_\text{F}$ become 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.