[Wien] 2 ways to calculate bindning energy

[Heinz Haas]

> Lyudmila Dobysheva wrote:
> > Tuesday 11 March 2008 21:02 B. Yanchitsky has written:
> >> Ev_super = E[N-1] - (N-1)*E[1].      (1)
> >> Ev_atom = Ei - E[1].                          (2)
> >
> > I cannot quite catch the problem: do you expect these values equal?

You are absolutely right:
(1) gives you (approximatly) the formation energy of a vacancy, in metal 
physics generally described as the energy required to move an atom from 
the inner area to the surface. For this reason also the simplistic 
argument of B.Y. is not correct. Even in the primitive model of isolated 
bonding one would get: Ev_atom = (Ei - E[1]) / 2.
(2) gives you (again very approximately) the formation energy of 
the crystal from free atoms.
Heinz Haas