CNDO/2 calculations were performed on the clusters X4H9 and X4Y9 modelling the [111] diamond and silicon surfaces. The x was either carbon or silicon atom and the Y was a pseudo-atom containing one sp3 hybrid orbital. It was shown that in the CNDO/2 approximation in the foregoing pseudo-atom models, the charge distribution of the cluster was better than the hydrogen atom, because the electronegativity of the hydrogen differs significantly from the electronegativity of the sp2 orbital of the silicon atom. Using the CNDO/2 parametrization, the electronegativity of the hydrogen was very near to the electronegativity of the sp3 orbital of the carbon atom, thus the hydrogen could be used for the saturation of the carbon clusters.

CNDO/2 Calculations of Relaxation and Reconstruction of Diamond and Silicon [111] Surfaces. I.Laszló: International Journal of Quantum Chemistry, 1982, 21[5], 813-22