Figures 7 to 10 depict plots of the density of
states as a function of the energy calculated by the
Density Functional Theory Method (DFT).
From Figures 3 to 10, the energy gaps of
pure α-quartz SiO2 and doped α-quartz Si1-xMx
O2 can be calculated by the HF and DFT methods as
summarized in Table 2.
From Table 2 it can be seen that the calculation
by the DFT method yielded values of Eg smaller
than those calculated by the HF method. The Eg of
doped α-quartz SiO2 was reduced in comparison to
pure α-quartz SiO2. This decrease in Eg should
result from the creation of localized states due to
transition metals in the gap.