[DFTB-Plus-User] Calculation of HOMO and LUMO levels

[Hemanth Haridas]

Thank you for your response. I am trying to calculate the HOMO and LUMO
levels of a DNA fragment at Gamma point. As per your advice, I tried
reassigning the occupation numbers of the fractionally occupied states, and
found that the last fully occupied state would be lying nearly 5 states
below the calculated Fermi level. However, my understanding is that Fermi
should be between the occupied and unoccupied levels for a non-metallic
system. Any pointers on this matter would be much appreciated.

Thank you for your time.

Yours sincerely,
Hemanth

On Tue, Jun 13, 2023 at 11:44 AM Bálint Aradi <aradi at uni-bremen.de> wrote:

> >
> > Thank you for your reply. However when I checked the band.out file, I
> > have few energies with fractional occupancy. And they lie below the
> > Fermi level.
>
> If you have fractional occupations such as for metallic systems, then
> HOMO and LUMO are somewhat ill defined concepts. Probably, the
> Fermi-level is the best thing you can have then. If you wanted, you
> still could do define a HOMO, of course, by counting which would be the
> highest occupied level, if you filled up all levels with integer number
> of electrons until all electrons had been used up, but I am unsure,
> whether that would be a very useful quantity.
>
> Best regards,
>
> Bálint
> >
> > On Tue, 13 Jun, 2023, 11:35 am Bálint Aradi, <aradi at uni-bremen.de
> > <mailto:aradi at uni-bremen.de>> wrote:
> >
> >     Dear Hemanth,
> >
> >     HOMO = highest occupied molecular orbital, LUMO = lowest unoccupied
> >     molelular orbital. Occupations of the molecular orbitals can be
> >     found in
> >     the band.out file. Both levels should be in the vicinity of the
> >     Fermi-level.
> >
> >     Best regards,
> >
> >     Bálint
> >
> >
> >     On 13.06.23 07:18, Hemanth Haridas wrote:
> >      > Dear all,
> >      >
> >      > I am trying to calculate the HOMO and LUMO levels of a molecule
> >     using
> >      > DTB+. However, I could only find Fermi energy in the detailed.out
> >     file.
> >      > The calculation was performed on the Gamma point. Any pointers on
> >     how to
> >      > calculate HOMO and LUMO levels would be much appreciated.
> >      >
> >      > --
> >      > *Hemanth H 18310019*
> >      > Research Scholar
> >      > IIT Gandhinagar
> >      >
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> >      >
> >
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> >
> >
> >     --
> >     Dr. Bálint Aradi
> >     Bremen Center for Computational Materials Science, University of
> Bremen
> >     http://www.bccms.uni-bremen.de/cms/people/b-aradi/
> >     <http://www.bccms.uni-bremen.de/cms/people/b-aradi/>
> >
> >
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>
> --
> Dr. Bálint Aradi
> Bremen Center for Computational Materials Science, University of Bremen
> http://www.bccms.uni-bremen.de/cms/people/b-aradi/
>
>
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-- 
*Hemanth H 18310019*
Research Scholar
IIT Gandhinagar
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