[Wien] ELF

fabien.tran at vasp.at fabien.tran at vasp.at
Fri Nov 4 22:20:46 CET 2022


It is on my to-do list to reimplement ELF in VASP in a more proper way. 
In any case, it seems that ELF was buggy in a certain number of codes 
(WIEN2k, VASP, Quantum Espresso).

On 04.11.2022 22:06, Kateryna Foyevtsova wrote:
> Hello,
> 
> since I see that VASP results are being discussed here, I'd like to
> bring your attention to my communication with the VASP developers in
> April this year:
> 
> https://www.vasp.at/forum/viewtopic.php?f=3&t=18484
> 
> where they admitted that "the current implementation depends strongly
> on the choice of the POTCAR. You can test this by using the GW POTCAR
> and will find contributions from Ni 3d electrons. We believe that with
> this pseudo-potential dependent ELF is not a good measure for
> electronic localisation and thus want to replace this (very old)
> implementation in a future release."
> 
> which means that ELF calculated in the current version (and all
> earlier versions, apparently) of VASP can have errors and should not
> be used as a gold standard. I think they still have not fixed that bug
> according to
> 
> https://www.vasp.at/forum/viewtopic.php?f=4&t=18628&p=22510&hilit=elf#p22510
> 
> Best,
> Kateryna
> 
> 
> On 2022-11-04 13:11, reyhaneh ebrahimi wrote:
>> [CAUTION: Non-UBC Email]
>> 
>> Dear Prof. Blaha
>> Thank you for your valuable answer to my Email.
>> I put my ELF graph, your ELF results, and Jiawang  and Olivier' graph
>> for SnSe on one page to have a better comparison, see
>> "https://www.mediafire.com/file/kyfi46ppx6mhtnx/SnSe-final.jpg/file".
>> I also specified the plane which I did my ELF calculation on it.
>> Therefore, as you mentioned in your Email, the existing differences
>> between my graph, your graph, and Jiawang  and Olivier' graph would be
>> due to the choice of different planes in these works.
>> Sincerely yours
>> Reyhaneh Ebrahimi
>> 
>> On Fri, Nov 4, 2022 at 8:33 AM Peter Blaha <peter.blaha at tuwien.ac.at>
>> wrote:
>> 
>>> Sorry: the links should be:  SnSe, not SnGe
>>> 
>>> http://www.wien2k.at/Depository/SnSe-f.png
>>> http://www.wien2k.at/Depository/SnSe-g.jpg
>>> http://www.wien2k.at/Depository/SnSe-t.png
>>> 
>>> Am 04.11.2022 um 15:27 schrieb Peter Blaha:
>>>> Your picture for SnSe is probably in a different plane as compared
>>> to
>>>> the 4 pictures in the paper.
>>>> I produced 2 elf pictures, which resembles the planes in Fig. 6f
>>> and 6g.
>>>> 
>>>> They look as expected. In the interstital identical (see eg. the 2
>>> 
>>>> different blue features in 6f), but inside the spheres quite
>>> different
>>>> because of the pseudopotentials.
>>>> 
>>>> I guess it is a general feature that inside spheres (and for
>>> heavier
>>>> atoms) the PP ELF is nonsense.
>>>> 
>>>> You can download them at:
>>>> 
>>>> http://www.wien2k.at/Depository/SnGe-f.png
>>>> http://www.wien2k.at/Depository/SnGe-g.jpg
>>>> http://www.wien2k.at/Depository/SnGe-t.png
>>>> 
>>>> 
>>>> Am 04.11.2022 um 00:13 schrieb reyhaneh ebrahimi:
>>>>> Dear Prof. Blaha
>>>>> I apologize. Let me make my previous Email a little more
>>> complete. As
>>>>> you mentioned in your Email, for SnS the sources of differences
>>>>> between the results of ELF using WIEN2k code and VASP code is due
>>> to
>>>>> the difference between all-electron and pseudopotentials
>>> calculations
>>>>> in these two codes. However, I am still not sure that the
>>> differences
>>>>> between my results for the ELF of SnSe and Jiawang and Olivier's
>>> paper
>>>>> are normal or not. I would be glad if you let me know your
>>> opinion
>>>>> about this subject.
>>>>> Sincerely yours
>>>>> Reyhaneh Ebrahimi
>>>>> 
>>>>> On Thu, Nov 3, 2022 at 1:13 PM Peter Blaha
>>> <peter.blaha at tuwien.ac.at
>>>>> <mailto:peter.blaha at tuwien.ac.at>> wrote:
>>>>> 
>>>>> Good to hear that this has been resolved.
>>>>> 
>>>>> PS: I just did a SnSe calc. and compared with the VASP paper.
>>>>> Similarly,
>>>>> very good agreement in the interstitial, while inside the
>>> atomic
>>>>> cores
>>>>> there is the expected difference between all-electron and
>>>>> pseudopotentials.
>>>>> 
>>>>> Am 03.11.2022 um 21:06 schrieb Kateryna Foyevtsova:
>>>>>> Dear Prof. Blaha,
>>>>>> 
>>>>>> I think I know what's going on with ELF. Wien2k gets it
>>>>> correctly, but
>>>>>> Quantum Espresso has a bug which shows up in nspin=1
>>>>> calculations. In
>>>>>> the attached figure I compare the wien2k result with two
>>> QE
>>>>>> calculations: (1) one with nspin=1 switch and (2) one with
>>> nspin=2
>>>>>> switch. In both cases I am looking at the same
>>> non-magnetic
>>>>> solution
>>>>>> that has the same energy in the two QE calculations.
>>>>>> 
>>>>>> Now you see that the difference between QE nspin=1 and
>>> nspin=2 is
>>>>>> dramatic whereas there should be none.
>>>>>> 
>>>>>> The wien2k result looks very similar to the QE nspin=2
>>> result
>>>>> in the
>>>>>> interstitial region at 0.5,0.5,0.0, marked with a big
>>> purple "X".
>>>>> There
>>>>>> are differences close to atomic nuclei but this is
>>> expected given
>>>>> that
>>>>>> we are comparing an all-electron and a pseudo-potenial
>>> code.
>>>>>> 
>>>>>> Thank you very much for helping me resolve this issue.
>>>>>> 
>>>>>> Best,
>>>>>> Kateryna
>>>>>> 
>>>>>> On 2022-11-02 12:21, Peter Blaha wrote:
>>>>>>> [CAUTION: Non-UBC Email]
>>>>>>> 
>>>>>>> My result looks like the attached picture. I do get 0.8
>>> in the
>>>>> core
>>>>>>> region of Ni, but not larger than that. It is probably
>>> similar
>>>>> than
>>>>>>> yours.
>>>>>>> I have no idea why it is different from QE, except maybe
>>> that
>>>>> these
>>>>>>> are pseudopotential calc.
>>>>>>> 
>>>>>>> As I said before, you should compare other compounds, and
>>> also
>>>>> compare
>>>>>>> with literature ELF calculations.
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> Am 01.11.2022 um 21:16 schrieb Kateryna Foyevtsova:
>>>>>>>> Dear Prof. Blaha,
>>>>>>>> 
>>>>>>>> thank you for looking into this issue. I've tried the
>>> modified
>>>>>>>> create_rho.f and calculated the ELF of NdNiO2 again
>>> using
>>>>> create_elf.
>>>>>>>> I am getting a better agreement with QE, but it is not
>>> perfect
>>>>> as you
>>>>>>>> noted it too. My calculation was well converged and I
>>> used the
>>>>> same
>>>>>>>> k-grid and RKmax=7. The bandstructures from QE and
>>> wien2k agree
>>>>> very
>>>>>>>> well.
>>>>>>>> 
>>>>>>>> I attach my comparison as a png file. I wonder whether
>>> you have
>>>>> any
>>>>>>>> idea about the possible reasons for the differences in
>>> ELF that
>>>>> the
>>>>>>>> two codes give? For example, at 0.5,0.5,0 the wien2k
>>> value is
>>>>> ~0.22
>>>>>>>> and the QE value is ~0.43.
>>>>>>>> 
>>>>>>>> Thank you,
>>>>>>>> Kateryna
>>>>>>>> 
>>>>>>>> On 2022-10-28 04:43, Peter Blaha wrote:
>>>>>>>>> [CAUTION: Non-UBC Email]
>>>>>>>>> 
>>>>>>>>> Dear Kateryna ,
>>>>>>>>> 
>>>>>>>>> In fact, I found a big difference between
>>> create_elf   and
>>>>>>>>> x lapw0 (with VX_ELF); x lapw5 -exchange
>>>>>>>>> 
>>>>>>>>> I traced it back to normalization errors in tau_w and
>>> tau_tf,
>>>>> which
>>>>>>>>> missed a factor of 2.
>>>>>>>>> 
>>>>>>>>> The attached    create_rho.f  fixes the problem. It
>>> should be
>>>>> copied
>>>>>>>>> into SRC_trig; make
>>>>>>>>> 
>>>>>>>>> Then you can use    create_elf   again.
>>>>>>>>> 
>>>>>>>>> PS: I would always compare the ELF created with both
>>> methods as
>>>>>>>>> indicated above. Depending on the numerics, one or the
>>> other
>>>>> method
>>>>>>>>> may give smoother plots, but in any case, they should
>>> be very
>>>>> similar.
>>>>>>>>> 
>>>>>>>>> PPS: The agreement to QE-ELF seems reasonable (but not
>>>>> perfect), but
>>>>>>>>> I've not converged my calculations.
>>>>>>>>> 
>>>>>>>>> Thanks for the report
>>>>>>>>> Peter Blaha
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>>> I attach a pdf showing the differences. Also attached
>>> are my
>>>>> wien2k
>>>>>>>>>> >struct file and quantum espresso input file.
>>>>>>>>> 
>>>>>>>>>> Both calculations were done without spin polarization
>>> and
>>>>> using PBE.
>>>>>>>>> 
>>>>>>>>>> To me, the differences are big enough to question
>>> whether
>>>>> it is
>>>>>>>>>> >meaningful to use ELF at all if it depends on
>>> all-electron vs
>>>>>>>>>> >pseudopotential so strongly. Unless I am missing
>>> something or
>>>>>>>>>> doing >something wrong.
>>>>>>>>> 
>>>>>>>>>> Thank you,
>>>>>>>>>> Kateryna
>>>>>>>>> 
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>>>>> --
>>>>> 
>>> 
>> --------------------------------------------------------------------------
>>>>> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060
>>> Vienna
>>>>> Phone: +43-1-58801-165300
>>>>> Email: peter.blaha at tuwien.ac.at
>>> <mailto:peter.blaha at tuwien.ac.at>
>>>>> WIEN2k: http://www.wien2k.at <http://www.wien2k.at>
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>>> <http://www.imc.tuwien.ac.at>
>>>>> 
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>>> --
>>> 
>> --------------------------------------------------------------------------
>>> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
>>> Phone: +43-1-58801-165300
>>> Email: peter.blaha at tuwien.ac.at    WIEN2k: http://www.wien2k.at
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> 
> --
> Kateryna Foyevtsova, PhD
> 
> Research Associate
> Stewart Blusson Quantum Matter Institute
> The University of British Columbia | Vancouver
> 261C - 2355 East Mall | Vancouver BC | V6T 1Z4 Canada
> Phone +1 (604) 822-8545
> foyevtsova at phas.ubc.ca
> 
> www.sbqmi.ubc.ca
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