[Wien] problems with convergence of SCF for AFM HoPtBi

Thu Nov 1 18:55:20 CET 2018

Dear Xavier,

"Fixed-Point" is the more mathematical term for "Self-Consistent". There is
a lot of interesting math behind "Self-Consistent" that is not apparent.
For instance, nasty oscillating problems may be related to what are called
"Strange Attractors" (e.g. https://en.wikipedia.org/wiki/Attractor). While
one hopes that scf problems converge nicely and cleanly, they don't have
to! (I don't have the math to understand how to avoid some of the really
nasty cases.)

Interesting point about Fourier transform, not sure how one would do this
transform. I will ponder.

On Thu, Nov 1, 2018 at 12:39 PM Xavier Rocquefelte <
xavier.rocquefelte at univ-rennes1.fr> wrote:

> Thank you so much Laurence for this explanation which definitely enlight
> my understanding!
>
> Could you just give me more hints. What do you mean by "fixed point
> solution" when you are speaking about the spins?
>
> Brainstorming session:
>
> I am a chemist but I can propose an idea without a clear understanding!
> The rotations are non-linear and we should find a way to express them in
> such a way to be linear.
>
> Is a Fourier transform (or fractional Fourier transform or something
> related) useful in such a case?
>
> Cheers
>
> Xavier
>
>
>
>
> Le 01/11/2018 à 17:19, Laurence Marks a écrit :
>
> Quite a few things are going on "Under the hood" in these systems, so let
> me explain a little.
>
> For heavy atoms with large RMTs the initial pseudocharge (PW density
> inside the RMTs) from dstart is quite bad. In addition, unless you are
> careful to chose a "good" initial spin state in case.inst, the spins can be
> quite far from the fixed point solution. While it might appear that the
> density and energy (:DIS and :ENE) are oscillating, in reality the
> pseudocharge and the spin/orbital moments are rotating slowly in a
> N-Dimensional space. Rotations are non-linear, and the mixer (all versions
> in all DFT codes to my knowledge) use linear expansions. It can therefore
> take a long time for these rotations tocomplete. What you will often see if
> you look at the pseudocharge (grep :CPC in 18.1, the pseudocharge was not
> monited in earlier versions as its role was not known) you will often see
> that it is slowly "walking" -- similarly the spin moments etc.
>
> When you add SOC and/or +U (or -eece) there will be large rotations of the
> spins and/or spin moments.
>
> In an ideal world some transformation would be applied to the Wien2k
> variables to separate the pseudocharge and convert the rotations to linear
> variables. I do not know how to do this, and simple ideas such as using the
> sum and difference of spins don't work. (As expected, since this is a
> linear transformation.) I am open to (mathematical)
> suggestions/inspirations. It has to be math not fudge -- the mixer only
> works when the math is right!
>
> On Thu, Nov 1, 2018 at 9:34 AM Xavier Rocquefelte <
> xavier.rocquefelte at univ-rennes1.fr> wrote:
>
>> I have exactly the same experience. It is really a matter of cooking to
>> my point of view and strongly depends on the system and what is
>> happening at the Fermi level.
>>
>> In my case I am using DFT+U+SOC for such systems. The hubbard term
>> indeed allows to separate the 4f states. However, the SOC is also
>> essential and leads to large effects in these systems.
>> In the case of HoPtBi, all the elements requires SOC. In addition it is
>> an intermetallic compound, meaning that you have both localized and
>> delocalized electrons!
>>
>> Did you try the following procedure:
>> - DFT+SOC in a self-consistent manner
>> - DFT+SOC+U on top of the first calculation
>>
>> Sometimes the lift of degeneracy due to SOC is sufficient to converge
>> more efficiently DFT+SOC and then after DFT+SOC+U. And sometimes it is
>> the other way around;)
>>
>> Best wishes
>> Xavier
>>
>>
>> --
>> ------------------------
>> Institut des Sciences Chimiques de Rennes (ISCR)
>> Univ Rennes - CNRS - UMR6226, France
>>
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__iscr.univ-2Drennes1.fr_cti_people_permanent-2Dstaff_rocquefelte-2Dxavier&d=DwICAg&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=V1_Z6_elFWMevjRRzb6Er-1CwhwNLWJ5nHzKWh26Fo0&s=adjkiyhXqoBS6b7SN1a8EitYiDIMwrzO8SLBzLqxJ0M&e=
>> ------------------------
>> ICAMM2019 : VASP Workshop and International Materials Modelling Conf
>> June 26-July 3 2019, Rennes France
>> icamm.2019.sciencesconf.org
>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__icamm.2019.sciencesconf.org&d=DwMF-g&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=7ofp_QFW3wtFVeJdOjORXFJkVocx5R67hVEjDMKs1gU&s=SWDltjKVqkNVzo-rRUsOgWLbEWnKJt7jxy-5CgNOTtU&e=>
>> : Registration opening soon, see you there!
>>
>> _______________________________________________
>> Wien mailing list
>> Wien at zeus.theochem.tuwien.ac.at
>>
>> https://urldefense.proofpoint.com/v2/url?u=http-3A__zeus.theochem.tuwien.ac.at_mailman_listinfo_wien&d=DwICAg&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=V1_Z6_elFWMevjRRzb6Er-1CwhwNLWJ5nHzKWh26Fo0&s=bHKBKCqE5r9Ol5EZoCphMsvUqWp9VPpa4qmZjlZ76MY&e=
>> SEARCH the MAILING-LIST at:
>> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.mail-2Darchive.com_wien-40zeus.theochem.tuwien.ac.at_index.html&d=DwICAg&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=V1_Z6_elFWMevjRRzb6Er-1CwhwNLWJ5nHzKWh26Fo0&s=QFcXH13Qr3d3q8iYQbINXbHncLwDP5UPJWJ9QJbhqIA&e=
>>
>
>
> --
> 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
> <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.cfw.org_100-2Dpercent&d=DwMF-g&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=7ofp_QFW3wtFVeJdOjORXFJkVocx5R67hVEjDMKs1gU&s=g4dhSPvrl6Wds0HFvbq2YAyvt-WxDrhVlLRuIOOy_DQ&e=>
> Co-Editor, Acta Cryst A
>
>
> _______________________________________________
> Wien mailing listWien at zeus.theochem.tuwien.ac.athttp://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien <https://urldefense.proofpoint.com/v2/url?u=http-3A__zeus.theochem.tuwien.ac.at_mailman_listinfo_wien&d=DwMF-g&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=7ofp_QFW3wtFVeJdOjORXFJkVocx5R67hVEjDMKs1gU&s=lKpdVmO5ijXykrKJjJGznjnOjstgOx2O6nFqj1TWU_4&e=>
> SEARCH the MAILING-LIST at:  http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.mail-2Darchive.com_wien-40zeus.theochem.tuwien.ac.at_index.html&d=DwMF-g&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=7ofp_QFW3wtFVeJdOjORXFJkVocx5R67hVEjDMKs1gU&s=X1tIMV_drYY66ujhdFv8IZ35JeONtOdvYSbN0cJEos0&e=>
>
>
> --
> ------------------------
> Institut des Sciences Chimiques de Rennes (ISCR)
> Univ Rennes - CNRS - UMR6226, Francehttps://iscr.univ-rennes1.fr/cti/people/permanent-staff/rocquefelte-xavier <https://urldefense.proofpoint.com/v2/url?u=https-3A__iscr.univ-2Drennes1.fr_cti_people_permanent-2Dstaff_rocquefelte-2Dxavier&d=DwMF-g&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=7ofp_QFW3wtFVeJdOjORXFJkVocx5R67hVEjDMKs1gU&s=IJ7bjHPrazGUpI7Svi-lZ80grMhgzalkAg_p7yYLUTE&e=>
> ------------------------
> ICAMM2019 : VASP Workshop and International Materials Modelling Conf
> June 26-July 3 2019, Rennes Franceicamm.2019.sciencesconf.org  : Registration opening soon, see you there!
>
>

-- 
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20181101/9df0efa7/attachment.html>