[Pw_forum] Electronic entropy

[Nicolas FERNANDEZ]

Thank you all for your replies !
Regards

Nicolas
> ----------------------------------------
> From: Lorenzo Paulatto <lorenzo.paulatto at impmc.upmc.fr>
> Sent: Wed Mar 27 10:15:34 CET 2013
> To: Nicolas FERNANDEZ <nicolas.fernandez at etu.univ-provence.fr>, PWSCF Forum <pw_forum at pwscf.org>
> Subject: Re: [Pw_forum] Electronic entropy
> 
> 
> On 03/27/2013 09:18 AM, Nicolas FERNANDEZ 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
> Dear Nicolas,
> if you convert 0.01Ry to Kelvin/Boltzmann_constant units you'll get that 
> it is equivalent to 1578.87 Ry, this is quite a high temperature!
> 
> This is because the smearing is only a computational trick, it's used to 
> converge the sum over the Brillouin zone faster. It's contribution to 
> the total energy is actually remove (that's why -TS) in order to get the 
> benefit of faster convergence without changing the final result. More 
> details: http://prb.aps.org/abstract/PRB/v40/i6/p3616_1
> 
> You could think about setting the smearing to an actual temperature 
> value, and remove the parts of the code that compensate for it (i.e. 
> putting the -TS back in). I don't know if this would be a meaningful 
> approach, it would require some thought to find out.
> > It (probably) corresponds to the temperature but the temperature of what?
> the fictitious temperature you set: 0.01 Ry
> > What is the temperature unit?
> Rydberg atomic units, you can convert to Kelvin via the Boltzmann 
> constant: k_B = 157887 Ry/K if I'm not mistaken
> > How to calculate or set it?
> you don't, you set it in order to converge the BZ sum without perturbing 
> the system too much
> > Is my approach correct to evaluate the electronic entropy?
> I don't know :)
> > Thank you for your responses.
> >
> > Best regards,
> 
> tchao
> 
> -- 
> Dr. Lorenzo Paulatto
> IdR @ IMPMC -- CNRS & Université Paris 6
> phone: +33 (0)1 44275 084 / skype: paulatz
> www:   http://www-int.impmc.upmc.fr/~paulatto/
> mail:  23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
>