Fig. 49 displays the band structure of the transition metals (the dotted line is the fermi energy). From
the left to the right the electron density increases and so the fermi energy moves up to the d bands.
But in every point the fermi energy hits the band somewhere. In the d bands the band width is very
small, which means that the matrix element we calculated in the tight binding model is fairly small.
That gives fairly flat bands and if we want to approximate something like parabolas it ends up that
we need a high effective mass (so in something with flat bands the electrons do not move through so
good). For example in copper the fermi energy cuts through the s band and all the d bands are filled.
So in copper all the narrow bands that have a high effective mass just are not contributing any more
and the fermi energy has moved up. The s band makes copper a good conductor. Fig. 50 shows the
Figure 49: Transition metals.dispersion relationship and the density of states of copper. The density of states of the d band has
some peaks in it. These peaks correspond to places in the dispersion relationship where there are a
lot of states at that energy.
Figure 50: Dispersion relationship and density of states of copper.