[Pw_forum] nondegenerate electrons in DFT.

[Nicola Marzari]

Jiayu Dai wrote:
> Dear Users,
>
> Recently, i was dealing with systems with nondegenerate electrons, that is, when
> T/T_F > 1 (T_F is the fermi temperature). I read some papers, and somebody said
> that the calculation for these system is prohibitive in DFT. I did not know why
> they said so. As my understanding, there is no limit in DFT to do with these
> system. Although electrons are fermi particles, but the fermi distribution promise
> the right states of electrons in the calculations.  And i did not find any
> explanation about this in the textbook of DFT in my hand.
>
> As an example, when the temperature is high enough, so that T/T_F is greater than
> 1, we can increase the bands window to deal with these cases, i think. Is it
> correct for my understanding? 
>
> Thanks a lot.
>
> Jiayu
>   

Correct - you would use Fermi-Dirac for the electronic occupations, and 
include
enough bands to make sure the the highest bands are almost empty.

This is the canonical extension to DFT according to Mermin (look at his 
Phys Rev papers
from the late 60s) - note that the true xc functional would be 
temperature-dependent, but
you would use a 0 temperature one. There might be early work (Singwi ?) 
on the matter.

                nicola


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Prof Nicola Marzari   Department of Materials Science and Engineering
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