[Wien] ELF

[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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>> 
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