Parametrization of the band structure of FCC crystals

The method consists in treating the integrals contained in the Hamiltonian matrix as independent parameters. With a starting set of approximated values of these integrals, the program evaluates the eigenvalues of the Hamiltonian matrix and calculates the mean value of the difference between them and the energy values of the bands to be fitted. The user has to give a limit to this difference; the program modifies the parameters until this limit is reached, finding at the end of the iterations the "best estimate" set of parameters which fits the true band.