Chemistry Reference
In-Depth Information
to consider what happens when an electric field is applied to the material.
An electric field will accelerate electrons to higher energies than the electrons
have when there is no field. In a metal, there are electronic states just above the
Fermi energy that can be populated by these accelerated electrons, and as a
result the material can readily conduct electricity. The result in Fig. 8.1
agrees with what you already knew about Ag—it is a metal.
The third numerical detail that is important in Fig. 8.1 arises from the fact
that Ag is a metal and the observation that the DOS is obtained from integrals
in
k
space. In Section 3.1.4 we described why performing integrals in
k
space
for metals holds some special numerical challenges. The results in Fig. 8.1
were obtained by using the Methfessel and Paxton smearing method to
improve the numerical precision of integration in
k
space.
Figure 8.2 shows a similar calculation of the electronic DOS for bulk Pt.
As for Ag, the Pt DOS is nonzero at the Fermi energy, indicating that Pt is a
metal. Two qualitative observations that can be made in comparing the DOS
of Ag and Pt are (i) Ag has its electronic states concentrated in a smaller
range of energies than Pt and (ii) Ag has a lower density of unoccupied
states above the Fermi energy than Pt. Both of these observations can be
loosely correlated with the physical observation that Pt is typically much
more chemically reactive than Ag.
Our next example is a different kind of material: silicon. Figure 8.3 shows
the calculated DOS for bulk Si from a DFT calculation using a two-atom
Figure 8.2
Similar to Fig. 8.1 but for bulk Pt.
