[DFTB-Plus-User] Is Fermi Level calculation reliable for molecules?

[Bálint Aradi]

Dear S. Chopra,

On 08/24/2018 07:35 AM, siddheshwar chopra wrote:
> Dear All,
> I am using DFTB+ for molecules and polymer studies. I need to study the
> states around the Fermi levels.
> I want to confirm if the Fermi level energy mentioned in the
> "detailed.out" file reliable?

Reliable in which sense?

The Fermi level you obtain in detailed.out is the chemical potential,
which is needed in order to obtain a neutral system (or a system with
the specified amount of net charges) while filling up the energy levels
according to the selected filling function.

In case, you have a system with a large gap and very low electronic
temperature, the position is numerically ill defined, as shifting the
Fermi level in the gap may leave the occupations numerically unchanged.

As soon as the gap is smalle enough or the temperature is high enough,
so that you have excitations (levels with less than 2 electrons below
the Fermi level and levels with more than 0 electrons above), the Fermi
level position is well defined.

  Best regards,

  Bálint


-- 
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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