[Wien] Finite temperature DFT: electronic free energy

[Peter Blaha]

Thanks for the bug report in init_lapw.

Please note: when the temperature (broadening) is set to zero, it will 
use automatically "room temperature" (0.0018 Ry).

On 05/15/2018 06:40 AM, Gavin Abo wrote:
> I think you found a bug in init_lapw.  The fix seems like it should be 
> simple though.  On line 498 in the init_lapw script in the sed command, 
> it looks like $fermit just needs changed to $fermits.
> 
> I made a patch file called init_lapw.patch [ 
> https://github.com/gsabo/WIEN2k-Patches/tree/master/17.1 ], which you 
> should be able to apply and try simply using:
> 
> username at computername:~/Desktop$ cd $WIENROOT
> username at computername:~/WIEN2k$ wget 
> https://raw.githubusercontent.com/gsabo/WIEN2k-Patches/master/17.1/init_lapw.patch
> username at computername:~/WIEN2k$ patch -b init_lapw init_lapw.patch
> patching file init_lapw
> 
> Maybe F is the :ENE (TOTAL ENERGY) in case.scf.
> 
> I tried following what a previous user did [ 
> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg10319.html 
> ] but with a quick TiC calculation using run_lapw in WIEN2k 17.1:
> 
> T = 1000 K = 0.00633 Ry
> init_lapw -b -fermits 0.00633
> TiC.scf::ENE  : ********** TOTAL ENERGY IN Ry = -1783.95041939
> TiC.output2:          Kb * T            =   0.00633000
> TiC.output2:          -T*Entr           =  -0.00054181
> 
> T = 0 K = 0.0 Ry
> init_lapw -b -fermits 0.0
> TiC.scf::ENE  : ********** TOTAL ENERGY IN Ry = -1783.94928338
> TiC.output2:          Kb * T            =   0.00180000
> TiC.output2:          -T*Entr           =  -0.00005329
> 
> F_1000K - F_0K = (E - T*S) - (E - 0) = -T*S = -1783.95041939 - 
> (-1783.94928338) = -0.001136 => -T*S = -0.001136
> 
> If -T*S divided by 2:
> 
> -T*S = -0.001136/2 = - 0.000568 <- This seems reasonably close to the 
> above -0.00054181 for T = 1000 K.
> 
> As I recall, the -T*S term was doubled in WIEN2k versions after 2014 [ 
> https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg10319.html 
> ].
> 
> Though, there may be a flaw in my above calculation.
> 
> On 5/14/2018 5:35 PM, Sabry Moustafa wrote:
>>
>> Hi;
>>
>> I am interested in the electronic free energy (F=E-TS) using the 
>> finite temperature DFT using Fermi-Dirac statistics (i.e., Mermin's 
>> extension to 0 K DFT) -- i.e., I am not just looking for Fermi-Dirac 
>> as a broadening/smearing technique. So,how this can be done in WIEN2k?
>>
>> It looks like I have to define "-fermits X" in the init_lapw command 
>> (where X= kT, in Ry). But when I did (T=1000K in my case):
>>
>> init_lapw -b -fermits 0.00633
>>
>> I got "fermit: Undefined variable." at the end. This is fixed though 
>> when defined fermit as well:
>>
>> init_lapw -b -fermit 0.00633 -fermits 0.00633
>>
>> So, do I have to define both?
>>
>>
>> Also, where can I find this "free energy F". It does not seem to be 
>> the "TOTAL ENERGY" in case.scf. Seems like I need to add this "TOTAL 
>> ENERGY" (E) to "-T*Entr" (-TS) in case.output2 file to get F?
>>
>>
>> Thanks ;
>>
>> Sabry
>>
>>
>> :-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:
>>
>> Sabry G. Moustafa, Ph.D.
>> Department of Chemical and Biological Engineering,
>> University at Buffalo, The State University of New York.
>> 511 Furnas Hall
>> Buffalo, NY 14260-4200
>> 716-645-1186 (office)
>> 716-239-8543 (cell)
>>
>> E-mail: sabrygad at buffalo.edu <mailto:sabrygad at buffalo.edu>
> 
> 
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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