Quantum phase transition in the Hartree-Fock wave function of the   hydrogen molecule
  Precise solutions of the Hartree-Fock equations for the ground state of the hydrogen molecule are obtained for a wide range of internuclear distances R by means of a two-dimensional fully numerical mesh computational method. The spatial parts of the single-electron wave functions are found to be coinciding for R<2.30a.u. At larger distances they become different and as R->\infty each of them takes the form corresponding to a separate atom. This quantum phase transition occurring at R=2.30a.u. gives a natural boundary between a delocalized behavior of electrons in the molecule and their distribution over separate atoms. This phenomenon can be also considered as an analog of the Wigner crystallization or the Mott transition on the level of a single molecule. 
Mikhail V. Ivanov