Some ask, what, why, why, how.

  The main problem lies in the fact that by using X-rays determined the crystal lattices of different materials, and why they are, and not the other is not yet known. For example copper crystallizes in the fcc lattice, and iron in the BCC, which when heated becomes FCC is used for heat treatment of steels. Copper by heating the crystal lattice does not change.
    The literature provides many factors influencing the crystallization so I decided to remove them as much as possible, and metal model of the article say so perfect, that is, all atoms are identical (pure metal) without inclusions without introduction, without defects, etc. using Hall effect and other data on the properties and calculations Ashcroft and Mermin-, my main determining factor in the type of lattice appeared core of the atom or ion, which has turned out as a result of the transfer of the electrons in the conduction band.
   It turned out that the metallic bond is due not only to the socialization of electrons, and the outer electrons and atomic cores, which determine the direction or type of crystal lattice.Changing the metal lattice type it may be associated with the transition of an electron in the conduction band or return it from this zone. The phase transition.I think that phase transitions are possible without changing the lattice type. For example copper. I suppose that in the conduction band can be in copper and one electron from an atom, or maybe two, depending on external conditions.