  A high quality amorphous silicon (a-Si) nanostructures has grown
experimentally to study the origin of light emission and the quantum
confinement effect in a-Si. The quantum confinement effect increases the band
gap of material as the size of quantum structure decreases, which results in a
blue shift in optical luminescence and energy absorption. Here we demonstrate
this effect using extended H\"uckel method to calculate fundamental band gap
and optical absorption energy of a-Si samples with various dot sizes. As
result, when the dot size was decreased from 2.2 to 1.0 nm, the absorption
spectra peak shifted toward higher energy from 2.278 eV to 3.856 eV.
