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<div class="moz-cite-prefix">On 03/27/2013 09:18 AM, Nicolas
FERNANDEZ wrote:<br>
</div>
<blockquote
cite="mid:733019424.66972.1364372330187.JavaMail.root@bureau-frontal1"
type="cite">
<pre wrap="">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
</pre>
</blockquote>
Dear Nicolas,<br>
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!<br>
<br>
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:
<meta http-equiv="content-type" content="text/html;
charset=ISO-8859-1">
<a href="http://prb.aps.org/abstract/PRB/v40/i6/p3616_1">http://prb.aps.org/abstract/PRB/v40/i6/p3616_1</a><br>
<br>
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.<br>
<blockquote
cite="mid:733019424.66972.1364372330187.JavaMail.root@bureau-frontal1"
type="cite">
<pre wrap="">It (probably) corresponds to the temperature but the temperature of what? </pre>
</blockquote>
the fictitious temperature you set: 0.01 Ry<br>
<blockquote
cite="mid:733019424.66972.1364372330187.JavaMail.root@bureau-frontal1"
type="cite">
<pre wrap="">What is the temperature unit? </pre>
</blockquote>
Rydberg atomic units, you can convert to Kelvin via the Boltzmann
constant: k_B = 157887 Ry/K if I'm not mistaken<br>
<blockquote
cite="mid:733019424.66972.1364372330187.JavaMail.root@bureau-frontal1"
type="cite">
<pre wrap="">How to calculate or set it? </pre>
</blockquote>
you don't, you set it in order to converge the BZ sum without
perturbing the system too much<br>
<blockquote
cite="mid:733019424.66972.1364372330187.JavaMail.root@bureau-frontal1"
type="cite">
<pre wrap="">Is my approach correct to evaluate the electronic entropy?</pre>
</blockquote>
I don't know :)<br>
<blockquote
cite="mid:733019424.66972.1364372330187.JavaMail.root@bureau-frontal1"
type="cite">
<pre wrap="">Thank you for your responses.
Best regards,
</pre>
</blockquote>
<br>
tchao<br>
<br>
<pre class="moz-signature" cols="72">--
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
www: <a class="moz-txt-link-freetext" href="http://www-int.impmc.upmc.fr/~paulatto/">http://www-int.impmc.upmc.fr/~paulatto/</a>
mail: 23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
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