I was wondering if there are tables for successive work functions for (solid state) metals? All I can find are work functions to remove 1 electron from the surface of a metal into vacuum (and to keep it there). However, I guess it gets harder to remove electrons the more electrons already have been removed, right?
Maybe there's a way to relate the work function to the average degree of ionization of the material... do you know if that is possible at all? I've heard about the Thomas-Fermi approximation which relates the mean degree of ionization to the electron-temperature and electron-density but that seems to be rather inaccurate.
Finally, I'd like to know your opinion: Is it harder to ionize a metal gas or a metal solid? Although most work functions are a little bit smaller than the (1st) ionization-energies of the same material in gaseous state but I still think ionization of solids is harder. Do you agree?