  The extended Falicov-Kimball model which contains hybridization between
localized level and conduction band has been studied using the exact
diagonalization method. We obtain the single-particle density of states and the
valency from this method and analyze the behaviors of valence transition and
activation gap. We find that the valence transition is continuous due to
hybridization, while the activation gap closes discontinuously. Moreover, the
onset of the valence transition and the closing point of the activation gap
mismatch each other. Our result is well consistent with the recent experiment
on SmB_6.
