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The nuclear structure of 14 N and 10 B nuclei are studied in framework two collective excitation approximations. The first approximation is hole-hole Tamm-Dancoff Approximation (hh TDA) and the second is hole-hole Random Phase Approximation (hh RPA). All possible single body states of the allowed angular momenta are considered in the 1s, 1p, 2s-1d, and 1f shells. The Hamiltonian is diagonalized in the presence of Warburton and Brown interaction (WBP). The calculated compared with experimental data for the energy levels and form factors of electron scattering.

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In this paper we try to give a reasonable account for the origin of the experimental optical energy gap E o of a-Si:H deduced from the plot due to Cody (1 2 2  vs. E). Using a realistic model density of states diagram for a-Si:H and the constant dipole matrix element assumption, and a reasonable definition of the real optical energy gap E G , a new theoretical equation for ε 2 (E) was derived. The plot of the square root of this function 1 2 2  as a function of the photon energy E for appropriate fitting parameters gives a straight line fit in the energy region of significance extrapolating to the energy axis at a value similar to the experimental optical gap but about 0.1 eV lower than the theoretical optical gap E G proposed in our paper. We conclude that the experimental optical gap E o does not necessarily coincide with any optical transition threshold in the density of states diagram of a-Si:H.