Fixed amplitudes tuned orbitals FATO model

Fixed amplitudes tuned orbitals (FATO) model 

Specificity of any semiempirical parametrization is that in the FA approximation the one-center energies Ea eq. (2.88) related to the carbon atom remain hybridization-independent (see below and [44] and [45]). This result which ultimately comes from the fact that in carbon the valence shell is half filled, distinguishes carbon among other elements. For that reason (in the FA approximation) only the resonance contribution to the total energy depends both on orientation (as in the FAFO model) and on the form of the hybridization tetrahedra. This considerably simplifies the derivation in the case of carbon atoms. For that reason we consider it separately. 

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