ELECTRONIC STRUCTURE AND MAGNETIC PROPERTIES - Density Functional Theory - page 191

2. Calculate the electronic DOS for bulk Ag 2 O after optimizing the structure
of this material. Use your calculations to check our claim that DFT calcu-
lations predict this material to be a metal.
3. Sketch three spin orderings analogous to the one shown in Fig. 8.9 d but
with nonzero net magnetic moment.
4. Co, MnBi, and MnF 2 are all magnetic materials. Determine whether they
are ferromagnetic or antiferromagnetic. How strongly does the magnetic
state of each material affect its lattice constant? MnBi forms the NiAs struc-
ture (space group R3m) and MnF 2 forms the rutile (TiO 2 ) structure.
5. Determine using calculations whether spin has any effect on the structure
and energy of the diatomic molecules N 2 ,O 2 , and CO.
6. The DFT calculations shown in Fig. 8.10 are valid for bulk Fe at T 0K.
At temperatures above the so-called Curie temperature, T c , Fe is no longer
ferromagnetic because of thermal effects on the spin order. Find an appro-
priate reference that tells you what metals in the periodic table are ferromag-
netic and what their Curie temperatures are.
FURTHER READING
For more details on the roles of metal impurities in silicon solar cells and
efforts to engineer materials that are less affected by these impurities,
see S. Dubois, O. Palais, M. Pasquinelli, S. Martinuzzi, and C. Jassaud, J. Appl.
Phys. 100 (2006), 123502, and T. Buonassisi, A. A. Istratov, M. A. Marcus, B.
Lai, Z. H. Cai, S. M. Heald, and E. R. Weber, Nature Materials 4 (2005), 676.
For an explanation of why DFT does not accurately predict band gaps, see J. P. Perdew
and M. Levy, Phys. Rev. Lett. 51 (1983), 1884 and L. J. Sham and M. Schluter,
Phys. Rev. Lett. 51 (1983), 1888. For a description of some correction methods,
see S. Lany and A. Zunger, Phys. Rev. B 78 (2008), 235104.
For a detailed discussion of the failure of DFT calculations to predict the semiconduct-
ing character of Ag 2 O and the application of “post-GGA” methods to overcome this
problem, see W.-X. Li, C. Stampfl, and M. Scheffler, Phys. Rev. B 68 (2003),
165412.
To learn more about charge decomposition methods for assigning atomic charges,
see G. Henkelman, A. Arnaldsson, and H. Jonsson, Comp. Mater. Sci. 36
(2006), 354.
The basic principles of magnetism are described in essentially every solid-state
physics text. A classic reference for this genre is C. Kittel, Introduction to Solid
State Physics , Wiley, New York, 1976. Several topics that focus more specifically
on magnetic phenomena are M. Getzlaff, Fundamentals of Magnetism , Springer,