Long range Coulomb forces and the behaviour of the chemical potential of   electrons in metals at a second order phase transition
  We give a general thermodynamic analyzis of the behaviour of the chemical potential of electrons in metals at a second order phase transition, including in our analysis the effect of long range Coulomb forces. It is shown, that this chemical potential can have a kink at T$_c$, both for fixed sample volume and fixed external pressure. The Coulomb term transfers the changes in chemical potential of the electrons into an experimentally observable shift of the surface potential if the sample is electrically connected to a ground potential. VSGD.93.9.th1 
D. van der Marel, D. I. Khomskii, G. M. Eliashberg