Spin spiral calculation and SCAN metaGGA
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Spin spiral calculation and SCAN metaGGA
Dear VASP developers,
I did spin spiral calculations with qvector = (0 0 0) for the CaCuO2 system with metaGGA SCAN functional (primitive cell, should result in ferromagnetic solution).
It yields a total energy of 45.3594 eV, but when doing collinear calculations (without setting NUPDOWN) it yields a total energy of 45.3204 eV (per 1 Cu).
I expect the total energy to be the same for both cases  what may cause this difference?
More importantly, in the same system, a spiral (0.5 0.5 0) that corresponds to a Ctype AF solution gives a much higher energy of 44.5841 eV than the (0 0 0) spiral above. This means the AF arrangement of CaCuO2 is not preferred in the spinspiral & metaGGA calculations, despite being energetically preferred for collinear metaGGA calculations.
Are the metaGGA functionals compatible with spinspiral calculations?
Or is there anything wrong with the INCAR settings?
I use VASP version 5.4.4.
I did spin spiral calculations with qvector = (0 0 0) for the CaCuO2 system with metaGGA SCAN functional (primitive cell, should result in ferromagnetic solution).
It yields a total energy of 45.3594 eV, but when doing collinear calculations (without setting NUPDOWN) it yields a total energy of 45.3204 eV (per 1 Cu).
I expect the total energy to be the same for both cases  what may cause this difference?
More importantly, in the same system, a spiral (0.5 0.5 0) that corresponds to a Ctype AF solution gives a much higher energy of 44.5841 eV than the (0 0 0) spiral above. This means the AF arrangement of CaCuO2 is not preferred in the spinspiral & metaGGA calculations, despite being energetically preferred for collinear metaGGA calculations.
Are the metaGGA functionals compatible with spinspiral calculations?
Or is there anything wrong with the INCAR settings?
I use VASP version 5.4.4.
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 Global Moderator
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Re: Spin spiral calculation and SCAN metaGGA
Dear mateusz_domanski,
I do not see any issues with your INCAR file for the noncollinear calculation. Could you please share your INCAR file for the collinear calculation and also the OUTCAR files so that I can try to reproduce the issue?
Sudarshan
I do not see any issues with your INCAR file for the noncollinear calculation. Could you please share your INCAR file for the collinear calculation and also the OUTCAR files so that I can try to reproduce the issue?
Sudarshan

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Re: Spin spiral calculation and SCAN metaGGA
Dear Sudarshan,
In the .zip file below I am sending inputs & outputs for both spiral and collinear calculations that I wrote about.
Mateusz
In the .zip file below I am sending inputs & outputs for both spiral and collinear calculations that I wrote about.
Mateusz
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Re: Spin spiral calculation and SCAN metaGGA
Dear Mateusz,
Thanks for the files. Here are some suggestions after I was able to reproduce your error: (1) could you please try switching off LSPIRAL and see if the energies are consistent with those from a vasp_std calculation? (2) increase ENINI to 520 (what you had for ENCUT)?
Sudarshan
Thanks for the files. Here are some suggestions after I was able to reproduce your error: (1) could you please try switching off LSPIRAL and see if the energies are consistent with those from a vasp_std calculation? (2) increase ENINI to 520 (what you had for ENCUT)?
Sudarshan

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Re: Spin spiral calculation and SCAN metaGGA
Dear Sudarshan,
Ad (1) yes, I have tried it, the energies of standard noncollinear calculations are pretty much consistent with collinear calculations.
The results are:
for (0,0,0) spiral solution in eV/Cu: collinear 45.320404 ; noncollinear 45.320593 ; spiral 45.359392
for (0.5,0.5,0) spiral solution in eV/Cu: collinear 45.390423 ; noncollinear 45.389018 ; spiral 44.669547
So the differences for noncollinear results are rather small: 0.2 meV/Cu difference for (0,0,0) spiral solution and +1.4 meV/Cu difference for (0.5,0.5,0) spiral solution.
But for spiral calculations, the differences vs collinear results are significant: 39.0 meV/Cu for (0,0,0) spiral and +720.9 meV/Cu for (0.5,0.5,0) spiral.
Ad (2) after increasing ENINI to 520 the issue still occurs as it yields 44.551631 eV/Cu for (0.5,0.5,0) spiral, so the difference is even bigger.
Mateusz
Ad (1) yes, I have tried it, the energies of standard noncollinear calculations are pretty much consistent with collinear calculations.
The results are:
for (0,0,0) spiral solution in eV/Cu: collinear 45.320404 ; noncollinear 45.320593 ; spiral 45.359392
for (0.5,0.5,0) spiral solution in eV/Cu: collinear 45.390423 ; noncollinear 45.389018 ; spiral 44.669547
So the differences for noncollinear results are rather small: 0.2 meV/Cu difference for (0,0,0) spiral solution and +1.4 meV/Cu difference for (0.5,0.5,0) spiral solution.
But for spiral calculations, the differences vs collinear results are significant: 39.0 meV/Cu for (0,0,0) spiral and +720.9 meV/Cu for (0.5,0.5,0) spiral.
Ad (2) after increasing ENINI to 520 the issue still occurs as it yields 44.551631 eV/Cu for (0.5,0.5,0) spiral, so the difference is even bigger.
Mateusz
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 Global Moderator
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Re: Spin spiral calculation and SCAN metaGGA
Just to confirm before I move to nonzero QSPIRAL: if you set do you get consistent results between noncollinear and collinear calculations for
Code: Select all
ENINI=520
Code: Select all
QSPIRAL = 0.0 0.0 0.0

 Newbie
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Re: Spin spiral calculation and SCAN metaGGA
No, for spiral (0,0,0) with ENINI=420 eV I get 39.0 meV/Cu (vs collinear), while for ENINI=520 I get 8.8 meV/Cu difference.do you get consistent results between noncollinear and collinear calculations for QSPIRAL = 0.0 0.0 0.0
Mateusz

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Re: Spin spiral calculation and SCAN metaGGA
Right, I see that you are using a different POSCAR for each run (the collinear and noncollinear calculation). Rerunning the collinear calculation with the same structure and gives me identically the same energy for zero QSPIRAL. Are you able to reproduce this behavior?
Sudarshan
Code: Select all
ENINI=520
Sudarshan

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Re: Spin spiral calculation and SCAN metaGGA
I use a supercell for nonspiral calculations (LSPIRAL = F) so that it enables calculating an equivalent to (0.5, 0.5, 0) spiral solution.Right, I see that you are using a different POSCAR for each run (the collinear and noncollinear calculation).
Yes, with a primitive cell for (0,0,0) spiral solution (LSPIRAL = T) and ENINI=520 eV, I get the same value of energy as in the noncollinear run for the primitive cell (difference around EDDIFF value). The energy difference with collinear calculation stays the same (some 0.2 meV).Are you able to reproduce this behavior?
Mateusz
Last edited by mateusz_domanski on Tue Jun 11, 2024 6:17 pm, edited 1 time in total.

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Re: Spin spiral calculation and SCAN metaGGA
Okay great thanks, so how I understand it now is: a collinear and noncollinear calculation give the same results when the the noncollinear case has LSPIRAL=.TRUE. QSPIRAL = 0.0 0.0 0.0 and ENINI matchining ENCUT for the same structure (not the supercell).
Now for QSPIRAL != 0.0, have you run a calculation where you set ENINI to 520 and ENCUT to 620 (commensurate with the +100 requirement in wiki/index.php/Spin_spirals)?
Sudarshan
Now for QSPIRAL != 0.0, have you run a calculation where you set ENINI to 520 and ENCUT to 620 (commensurate with the +100 requirement in wiki/index.php/Spin_spirals)?
Sudarshan

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Re: Spin spiral calculation and SCAN metaGGA
Yes, I did such a calculation  with (ENCUT 620, ENINI = 520) it yields 11.7 meV/eV vs collinear one with the same ENCUT (and the same POSCAR).Now for QSPIRAL != 0.0, have you run a calculation where you set ENINI to 520 and ENCUT to 620 (commensurate with the +100 requirement in wiki/index.php/Spin_spirals)?
Mateusz

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Re: Spin spiral calculation and SCAN metaGGA
Right, but in this case we would not expect a match between the collinear and noncollinear calculations (i.e. for QSPIRAL != 0)?
Sudarshan
Sudarshan

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Re: Spin spiral calculation and SCAN metaGGA
Dear Sudarshan, that was just FYI  I would expect these to match, but they may not match each other as these are two different computational methods  that is not really a problem.
You have asked me about zero spirals, but I do not see a big problem there, these results are pretty consistent.
However, I expect the energy differences between (0,0,0) and (0.5, 0.5, 0) spirals from spiral calculations and equivalent collinear calculations (in a supercell, I sent you these in my 2nd post) to be generally equal.
The issue is they are not.
In collinear calculations (0.5, 0.5, 0) spiral equivalent has 70.0 meV/Cu energy compared to (0,0,0) spiral equivalent.
In spiral calculations (0.5, 0.5, 0) spiral has +689.8 meV/Cu energy compared to (0,0,0) spiral.
That is a huge mismatch between these two results. The result for spiral calculations with SCAN (especially 0.5, 0.5, 0) does not seem rational (as AF groundstate is expected).
For GGA+U calculations these two energy differences match each other  with the collinear approach, the difference is 185.9 meV/Cu, while for the spiral method it is 181.4 meV/Cu.
That is a level of mismatch that I would expect.
Since there is such a large error in spiral calculations with metaGGA I am asking:
You have asked me about zero spirals, but I do not see a big problem there, these results are pretty consistent.
However, I expect the energy differences between (0,0,0) and (0.5, 0.5, 0) spirals from spiral calculations and equivalent collinear calculations (in a supercell, I sent you these in my 2nd post) to be generally equal.
The issue is they are not.
In collinear calculations (0.5, 0.5, 0) spiral equivalent has 70.0 meV/Cu energy compared to (0,0,0) spiral equivalent.
In spiral calculations (0.5, 0.5, 0) spiral has +689.8 meV/Cu energy compared to (0,0,0) spiral.
That is a huge mismatch between these two results. The result for spiral calculations with SCAN (especially 0.5, 0.5, 0) does not seem rational (as AF groundstate is expected).
For GGA+U calculations these two energy differences match each other  with the collinear approach, the difference is 185.9 meV/Cu, while for the spiral method it is 181.4 meV/Cu.
That is a level of mismatch that I would expect.
Since there is such a large error in spiral calculations with metaGGA I am asking:
MateuszAre the metaGGA functionals compatible with spinspiral calculations?