Analytical expression for formation energy

MrFrenkel

Hey folks,

I'm using Molecular Dynamics to calculate the formation energy of an interstitial in FCC metal.
Basically what I did is to minimize the perfects structure, and then find the minimized energy of the lattice with [100] dumbbell interstitial, to get the difference in energies.

I want to compare the result to analytical solution by calculating the two energies with local density dependent interaction energies, but I haven't found these expressions in Ashcroft nor Kittel.

Since i'm not a Materials Physicist\Chemist, I'm quite stuck... Does any of you know where I can find the appropriate analytical expressions ?

Thanks,