 Solution

With one valence electron per atom, the electron number density is $n=4/a^3$. For a spin-degenerate, three-dimensional free electron model at zero temperature,Substitution givesCopper has the larger Fermi wavevector and Fermi energy because its smaller cell gives a larger electron density. The energies are measured from the bottom of the free-electron dispersion, not from vacuum. Treating these real metals as monovalent free-electron systems is the model assumption, not a statement that their filled d bands are absent.