[Wien] Fermi Energy Calculation using WIEN2k

[Amlan Ray]

Dear Prof. Blaha,
I am asking you a question about the Fermi energy given by WIEN2k code in .scf output file. For metals, it gives a positive energy similar to what one expects from a free electron gas model (assuming the entire energy is kinetic energy). The calculated Fermi energy will depend on the reference point (zero energy). I think WIEN2k's reference point is the energy at the surface of overlapping Muffin-tin spheres. Since the electronic wave function at the surface of the overlapping Muffin-tin spheres matches with a plane wave function that is assumed for the electrons in the interstitial space, this reference point would define the energy of the lowest occupied single particle state for the electrons in the interstitial space in the context of the calculation. That means the Fermi energy calculated by the WIEN2k code (as given in .scf output file) is the energy difference between the highest occupied state in the interstitial space (Fermi level) and the lowest occupied state for the electrons in the interstitial space. This will be a positive energy similar to the Fermi energy obtained from a free electron gas model, however, of course, the Fermi energy calculated by WIEN2k code would include potential energy contribution also. 
Please let me know if this interpretation is correct.
With best regardsAmlan RayVariable Energy Cyclotron CenterKolkata, India
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