[Wien] Magnetocrystalline anisotropy

Tue Jan 16 15:26:04 CET 2018

Dear Xavier,

One other suggestion, with a caveat. In general if the physical model
is weak/wrong or there are coding errors, the convergence is poor.
This has to do with what I call "noise" in the calculation (for want
of a better term). Since the mixing is implicitly a Simplex derivative
noise matters.

The first caveat is that there can be large change in the orbital
occupancies with -so/orb. This is a rotation of the density matrix or
orbital potential, and rotations are poorly handled in Taylor
expansions (which all mixers are).

The second caveat is that when one reduces symmetry there can be
additional soft modes which only poorly converge.

On Tue, Jan 16, 2018 at 8:09 AM, Xavier Rocquefelte
<xavier.rocquefelte at univ-rennes1.fr> wrote:
> Dear Laurence
>
> Here is the point. Our results show that in version 17 a problem occurs
> related to the time-reversal, which appears only if we do GGA+U or EECE.
>
> a) The calculations we showed are already done in P1. Indeed, I wanted
> to avoid any problems related to symmetry.
>
> b) we (me and my PhD student William Lafargue-dit-Hauret) were exactly
> working along this line ... our preliminary results are not consistent.
>
> c) we didn't try this option ... we will try
>
> Thank you for your quick reply Laurence
>
> Best Regards
>
> Xavier
>
>
>
> Le 16/01/2018 à 15:03, Laurence Marks a écrit :
>> I may annoy Peter with the comment below, so it goes....
>>
>> Personally I have some reservations about the consistency between the
>> orbital potential and time-reversal operations in -so. Three possible
>> tests:
>>
>> a) Reduce the symmetry to P1 and run. While this is slower, I believe
>> your test case is small so this should not matter.
>> b) Hack the runsp_lapw script so that -orb is applied to lapw1, not in lapwso
>> c) Run without the up/dn component (-noorbud)
>>
>> On Tue, Jan 16, 2018 at 7:50 AM, Xavier Rocquefelte
>> <xavier.rocquefelte at univ-rennes1.fr> wrote:
>>> Here is a document showing the results graphically.
>>>
>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__filesender.renater.fr_-3Fs-3Ddownload-26token-3D8ac3a214-2Dedfa-2D4894-2Dfa1f-2D27aba5a5522f&d=DwIGaQ&c=yHlS04HhBraes5BQ9ueu5zKhE7rtNXt_d012z2PA6ws&r=U_T4PL6jwANfAy4rnxTj8IUxm818jnvqKFdqWLwmqg0&m=mfZINSS9VKVdzwe4U7cSmx0-ziyAHYu8JU6ZTl7KjeM&s=4O827iUX43sWWhwFi99lMba-6xHX3nxPAXPuikEN73k&e=
>>>
>>> It really looks like the problem we had before (using bad kmesh).
>>>
>>> We test it on two different compounds and in both cases WIEN2k_16 gives a
>>> correct picture and not WIEN2k_17.
>>>
>>> We are now comparing the two versions of the code.
>>>
>>> Regards
>>>
>>> Xavier
>>>
>>>
>>> Le 16/01/2018 à 12:10, Xavier Rocquefelte a écrit :
>>>
>>> Dear All
>>>
>>> Finally the problem is not completely solved.
>>>
>>> More precisely, when we are doing GGA+SO calculations and using a correct
>>> kmesh (no temporal symmetry), we obtain a symmetric magnetocrystalline
>>> anisotropy, namely same MAE along [0 1 0] and [0 -1 0].
>>>
>>> In contrast, when we are doing GGA+U+SO or EECE+SO with a correct kmesh we
>>> still obtain non-symmetric MAE, namely MAE along [0 1 0] and [0 -1 0] are
>>> different.
>>>
>>> In addition, the so obtained MAE looks similar to the ones obtained in
>>> GGA+SO with a bad kmesh (including temporal symmetry).
>>>
>>> At this moment, we are checking all the recent modifications in SRC_ORB and
>>> SRC_LAPW2 related to the manipulation of case.vorbup, case.vorbdn and
>>> case.vorbud files.
>>>
>>> Surprisingly, the EECE+SO calculations in WIEN2k_16 are symmetric, while not
>>> in WIEN2k_17.
>>>
>>> Next soon ... I hope.
>>>
>>> Xavier
>>>
>>>
>>> Le 10/01/2018 à 15:10, Xavier Rocquefelte a écrit :
>>>
>>> Dear All
>>>
>>> The problem is solved and was related to one stupid human mistake.
>>>
>>> It was necessary to generate a kmesh without adding inversion
>>> (time-inversion symmetry).
>>> Indeed, as mentionned in the userguide when using kgen program:
>>>
>>> "add inversion" ? This is asked only when inversion is NOT present.
>>>
>>> Say "YES" in all cases except when you do spin-polarized (magnetic)
>>> calculations WITH spin-orbit coupling (this breaks time-inversion symmetry
>>> and thus one MUST NOT add inversion symmetry (eigenvalues at +k and -k may
>>> be different).
>>>
>>> If you properly generate the kmesh for the spin-orbit calculations by doing
>>> : x kgen -fbz, then you obtain a symmetric magnetic anisotrop. In conclusion
>>> the asymmetry I obtained was due to an improper definition of the kmesh
>>> (adding artificially time-inversion).
>>>
>>> I want to thank all the participants who answered to my question. It was
>>> essential to identify such a mistake which has a huge impact on the results.
>>>
>>> Best wishes
>>>
>>> Xavier
>>>
>>>
>>>
>>> Le 10/01/2018 à 10:47, Xavier Rocquefelte a écrit :
>>>
>>> Dear Lyudmila
>>>
>>> The fact we have a small angle with axes is expected (also observed
>>> experimentally). It is related to the monoclinic symmetry of the system
>>> which permits it. However, you gave me an idea that I will test now and
>>> comment soon ;)
>>>
>>> Cheers
>>>
>>> Xavier
>>>
>>> Le 10/01/2018 à 10:40, Lyudmila a écrit :
>>>
>>> 10.01.2018 13:36, Lyudmila wrote:
>>>
>>> I see in the FM calculation also a slightly non-symmetric curve, isn't it?
>>>
>>>
>>> I meant the small angle with axes.
>>>
>>> Best wishes
>>> Lyudmila Dobysheva
>>>
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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