Why is DFT not used in calculating electronic structures and properties of metals? I know DFT calculations are not accurate for metallic structures. Can someone explain why?
Density Functional Theory (DFT) is used to calculate the electronic structure and properties of metals as much and "successfully" as it is used for molecules, clusters, alloys, insulators and semiconductors. Of course there are certain things that DFT is good at and can and cannot do. However saying that "DFT calculations are not accurate for metallic structures" is not correct.
Please have a look at the paper published relatively recently in Science with title "Insights into Current Limitations of Density Functional Theory" where the authors say and I quote
What are some of the major failures in DFT calculations?
First, they underestimate the barriers of chemical reactions, the band gaps of materials, the energies of dissociating molecular ions, and charge transfer excitation energies. They also overestimate the binding energies of charge transfer complexes and the response to an electric field in molecules and materials. ...all of these diverse issues share the same root —the delocalization error of approximate functionals, due to the dominating Coulomb term that pushes electrons apart.
Furthermore, typical DFT calculations fail to describe degenerate or near-degenerate states, such as arise in transition metal systems, the breaking of chemical bonds, and strongly correlated materials. All of these problems are merely manifestations of another common error —the static correlation error of approximate functionals.
DFT can theoretically depict the ground state of any material, however, we can only deal with the properties of material by using some approximation. the quality of your approximation determines the degree of accuracy.