Dear Mikko,

Your questions remained unanswered till i came. Your questions is related to the energy level diagram of a material. The electron energy levels inside a material is measured with reference to the vacuum level or the free electron level Evac. There are some distinguished electron energy levels in the material:

- The valence band edge level which lies under the vacuum level by the electron affinity Xa in eV,

- There is also the Fermi level which lies normally in the energy gap for degenerate material with the level designated by Ef

- There is also the valence band edge which lies under conduction band edge by the energy gap Eg

In metal there is only the Fermi level which is the highest occupied energy level at zero kelvin.

The work function is the energy given to the electron to raise it from the fermi level to the vacuum level.

So the work function phi= Evac- Ef,

It is also so that the the fermi level is termed the chemical potential of the material. Measured to vacuum level the chemical potential= (Ev-Ef)/-q,

with q the electronic charge.

Best wishes