The electron densities of pseudorelativistic eigenfunctions are smooth   away from the nuclei
  We consider a pseudorelativistic model of atoms and molecules, where the kinetic energy of the electrons is given by $\sqrt{p^2+m^2}-m$. In this model the eigenfunctions are generally not even bounded, however, we prove that the corresponding one-electron densities are smooth away from the nuclei. 
S{\o}ren Fournais and Thomas {\O}stergaard S{\o}rensen