Optical bandgap is obtained from UV/Vis spectra as the lowest transition
(or excitation) energy from the ground state to the first dipole-allowed
excited state. It is an implicit assumption that the lowest singlet
excited state can be described by only one singly excited configuration,
wherein an electron is promoted from the HOMO to the LUMO
However, the energy difference HOMO LUMO could consider more of one
electron.
Even though, as Abhishek says, DFT can provide trend
El 3/4/2011 3:10 PM, Abhishek Sharma escribió:
If you used DFT method to obtain band structure than always remember a
concept that DFT underestimate band gap, however it can provide trend
in variation of band gap for different systems.
Abhishek Sharma
On Fri, Mar 4, 2011 at 7:31 PM, Roberto Guerra <[email protected]
<mailto:[email protected]>> wrote:
Hello,
I calculated the band structure of bulk amorphous silicon (64 atoms
tetrahedrically coordinated). I found an HOMO-LUMO band gap of
about 0.7 eV.
Then I performed the OpticalCalculation, but I have that the resulting
imaginary dielectric function has a peak at E<0.7. How is this
possible? I
expect that each valence-to-conduction transition must be larger
than the
bang-gap!
Roberto
--
Gregorio García Moreno
PhD student
Department of Physical and Analytical Chemistry
University of Jaén
