All discussions in this chapter are based on the use of the fully relativistic version of the Kubo-Greenwood equation, see Chapter 16,

σμμ = ~πV Tr ³ Jˆμ Im Gˆ+(EF )Jˆμ Im Gˆ+(EF )

´ (17.1)

Jˆμ being the μ-th component of the current operator, μ ∈ (x, y, z), V the characteristic volume, and Gˆ+(EF ) referring to the positive side-limit of the resolvent of a single particle (Kohn-Sham) Dirac Hamiltonian.