[Wien] questions

[Stefaan Cottenier]

> Somebody can briefly explain me what is band regid model.

The assumptions that solids made from elements that are adjacent in the
periodic table have identical band structures, only with the Fermi energy
shift to the right for the heavier element.

>Another question, I noticed that for certain calculation one has negative
Fermi energies and
>for others it is positive!!! Which is the reason for that ???

The 'zero' to which the Fermi energies calculated by wien refer is defined
as the average of the potential in the interstitial region (see UG).
Sometimes E_F is above, sometimes below that reference point. This 'zero'
has not a nice physical meaning as the zero for free atoms (potential at
infinity -- in an infinite crystal you still have atoms at infinity...)

Stefaan