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 & Universit? Paris 6 phone: +33 (0)1 44275 084 / skype: paulatz www: http://www-int.impmc.upmc.fr/~paulatto/ mail: 23-24/4?16 Bo?te courrier 115, 4 place Jussieu 75252 Paris C?dex 05 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20130327/cd9ad75c/attachment.html
