[Wien] Finite temperature DFT: electronic free energy

Thu May 17 22:35:50 CEST 2018

On Thu, May 17, 2018 at 2:38 PM, Sabry Moustafa <sabrygad at buffalo.edu>
wrote:

>
> (0) PROBLEM:
> WIEN2k did not accept lage temperatures (>~4000 K). I always get this
> error "FERMI5 - Error" in the job error file. No complain in the
> init_lapw step; only after run_lapw finishes. Any help here?
>

No great surprise! If you are using this to improve convergence -- don't.
With the Wien2k mixer I have found little evidence that this helps in most
cases and in many cases it degrades convergence. Be careful about
transferring "lore" from Vasp to Wien2k.

If you want to calculate real parameters at 4000K or higher then you need
to look at real high-temperature functionals (which may be in LIBXC, or may
not).

>
>
> (1) Thanks Blaha and Gavin for your help -- I tried it and worked fine.
> Gavin, please note that in Fermi-Dirac statistics the energy is
> temperature dependent. See for example Marzari's thesis (e.g., Fig 4.2):
> https://urldefense.proofpoint.com/v2/url?u=http-3A__
> theossrv1.epfl.ch_Main_Theses-3Faction-3Ddownload-26upname-
> 3DMarzari-5Fthesis-5F1996.pdf&d=DwIGaQ&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNX
> t_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=
> QWFxBxDVokCVrWNwIw0tPvBInPWUpwTiF5I7NxLxYpY&s=
> cdlLD1tVxFmf0KY08zyP2A64jvG2mBpWzj8mZLsI9Qw&e=
>
> Of course.

>
> (2) Actually, the "TOTAL ENERGY IN Ry" in case.scf is the free energy
> F(T); i.e., F(T)=E(T) - T*S(T). This is written explicitly in the UG,
> when talking about "TEMPS" (Sec. 7.8.3):
> "The total energy is corrected by -TS ..."
> So, E(T) can be obtained from F(T) and -T*S(T), i.e., E = F + TS.
>
> The energy output using TEMPS is E = F + TS, no entropy corrections are
appropriate for the Mermin functional. (The UG is a little ambiguous.)

For reference, TEMP is not recommended for PORT, TEMPS should be used.
(TEMP can lead to erroneous results as the energy and forces are not
completely consistent.) It does not matter with MSR1a since this does not
use the energies.

> (3) Since I am beginner and familiar more with VASP at this point, I
> checked (using hcp-Fe crystal) both F(T) and -T*S(T) from both and found
> them to be consistent!
>
> I am not sure what this means. TEMPS is the Mermin functional with the
electronic entropy correctly included.

>
> Thanks;
> Sabry
>
> On 05/15/2018 03:34 AM, Peter Blaha wrote:
> >
> > 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 $fermits.
> >>
> >> I made a patch file called init_lapw.patch [
> >> https://urldefense.proofpoint.com/v2/url?u=https-3A__github.
> com_gsabo_WIEN2k-2DPatches_tree_master_17.1&d=DwIGaQ&c=
> yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_
> T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=QWFxBxDVokCVrWNwIw0tPvBInPWUpw
> TiF5I7NxLxYpY&s=4eJpf4P5rc-owCyY2z0A6f4LwLXfyV53RoirzxKM0Ng&e= ], which
> you
> >> should be able to apply and try simply using:
> >>
> >> username at computername:~/Desktop$ cd $WIENROOT
> >> username at computername:~/WIEN2k$ wget
> >> https://urldefense.proofpoint.com/v2/url?u=https-3A__raw.
> githubusercontent.com_gsabo_WIEN2k-2DPatches_master_17.1_
> init-5Flapw.patch&d=DwIGaQ&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNX
> t_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=
> QWFxBxDVokCVrWNwIw0tPvBInPWUpwTiF5I7NxLxYpY&s=JTU0K_
> FuSjQMbKJ3T_PkRcYRnJeSFWlJ4r-I9glbang&e=
> >> 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://urldefense.proofpoint.com/v2/url?u=https-3A__www.
> mail-2Darchive.com_wien-40zeus.theochem.tuwien.ac.at_
> msg10319.html&d=DwIGaQ&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_
> T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=QWFxBxDVokCVrWNwIw0tPvBInPWUpw
> TiF5I7NxLxYpY&s=RrAVLEV5tqysZLt_rsnLOkoND5UV7q-Ef1ZnXC3d0yk&e=
> >> ] 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://urldefense.proofpoint.com/v2/url?u=https-3A__www.
> mail-2Darchive.com_wien-40zeus.theochem.tuwien.ac.at_
> msg10319.html&d=DwIGaQ&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_
> T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=QWFxBxDVokCVrWNwIw0tPvBInPWUpw
> TiF5I7NxLxYpY&s=RrAVLEV5tqysZLt_rsnLOkoND5UV7q-Ef1ZnXC3d0yk&e=
> >> ].
> >>
> >> 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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> >
>
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-- 
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Gyorgi
www.numis.northwestern.edu ; Corrosion in 4D: MURI4D.numis.northwestern.edu
Partner of the CFW 100% program for gender equity, www.cfw.org/100-percent
Co-Editor, Acta Cryst A
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