Calculation of parameters in model Hamiltonians

The ab initio calculation of parameters of the Anderson model is illustrated within the framework of a simple, exactly solvable, model of a 3d compound. It is shown how the latter model can be mapped onto a simpler model, by projecting out degrees of freedom, and by including these degrees of freedom implicitly as a renormalization of parameters. For the model studied this approach is shown to be exact in the limit when the projected degrees of freedom correspond to very delocalized electrons.