[Pw_forum] Electronic entropy

[Matteo Cococcioni]

Dear Nicolas

If you use the smearing=FD the degauss parameter is the electronic
temperature (T) that gives you a measure of the (physical) broadening
of the Fermi distribution function (the deviation from its 0 K step
shape). if you use other smearing schemes degauss still measures the
smearing width of your (generalized) distribution function but does
not correspond exactly to the physical temperature anymore.
Generalized distribution functions (instead of FD) are used for
numerical convenience (i.e. to reduce the dependence of the total
energy on the smearing, particularly useful if you want to recover the
physics at 0 K). Useful reference:
DOI:10.1103/PhysRevB.51.6773
See also refs 16 and 17 quoted therein.

regards,

Matteo




On Wed, Mar 27, 2013 at 3:18 AM, Nicolas FERNANDEZ
<nicolas.fernandez at etu.univ-provence.fr> wrote:
> Dear all,
>
> I try to evaluate the electronic entropy contribution to the vacancy formation.
>
> I used smearing with Fermi-Dirac function and a degauss value of 0.01 Ry
>
> A line in the output file look very promising to calculate entropy :
>         smearing contrib. (-TS)   =      -0.11576742 Ry
> but I have a doubt about the "T" term.
> It (probably) corresponds to the temperature but the temperature of what?
> What is the temperature unit?
> How to calculate or set it?
> Is my approach correct to evaluate the electronic entropy?
>
> Thank you for your responses.
>
> Best regards,
>
> Nicolas
> PhD student
> Aix-Marseille University
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-- 
Matteo Cococcioni
Department of Chemical Engineering and Materials Science,
University of Minnesota
421 Washington Av. SE
Minneapolis, MN 55455
Tel. +1 612 624 9056    Fax +1 612 626 7246