In a lot of the literature, we see plots of the energy band structure from DFT simulations. How are these eigen-energies obtained as function of crystal momentum within the DFT framework? Are they the physical quasiparticle energies of the system, or are they just the eigen-energies of the Kohn-Sham equation?
Answer
we see plots of the energy band structure from DFT simulations. How are these eigen-energies obtained as function of crystal momentum within the DFT framework?
It depends on what specific software program was used to do the calculation.
Are they the physical quasiparticle energies of the system or just the eigen-energies of the Kohn-Sham equation?
Well, they can't actually be true physical quasiparticle energies... since calculating those would require, e.g., knowledge of the full many-body self-energy.
Some software just calculates the Kohn-Sham eigenvalues and says that those are "close enough" to the quasiparticle energies. Some software will throw in a little "self energy" correction.
But, typically, the Kohn-Sham eigenvalues are just assumed to be "close" to the quasiparticle self-energies and the band structure is based on kohn-sham eigenvalues. Of course, this is a horrible assumption in many cases... and a shockingly good assumption in other cases.
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