Roberto,
The band structure appears not to be totally correct. Seeing your input file
systlab.fdf, I realized that this curve is obtained under the gamma
point.approximation
Try to sample the Brillouin zone as follows:
%block kgrid_Monkhorst_Pack
2 0 0 0.0
0 2 0 0.0
0 0 2 0.0
%endblock kgrid_Monkhorst_Pack
Optical calculations:
%block Optical.Mesh
2 2 2
%endblock Optical.Mesh
These changes will make the calculation slightly heavier but that's the price
to pay for something more accurate.
I have a question regarding the choice of CG for the relaxation of your
structure. In your case, it seems that the use of the molecular dynamics such
as Nose, NPR,..... is more appropriate.
Hope this helps
Karim
> Indirect (band structure attached)
>
> R
Roberto:
sorry for this question, but are you sure that this band structure
corresponds to your 64-at calculation? I'd expect much more bands
and much less dispersion with 64 at. supercell.
(I did not count the bands per energy interval, though,
so I might be wrong).
Anyway: how does your total DOS look like?
Best regards
Andrei Postnikov
>
> In date 4/3/11 15:23:46, karim rezouali wrote:
>> Dear,
>>
>> Is the material under study (ie, bulk amorphous silicon) has a direct
>> electronic gap or not?
>>
>> Karim
>>
>>
>> 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
>
