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Spin-orbit interaction and electron structure in NCDFT
Date: 2017/10/25 05:43
Name: Daniil

Dear developers,

We are trying to reproduce the atomic state of Niobium with the OpenMX package. However, it seems that the spin-orbit interaction does not work like expected. For comparison, we performed 4 calculations: with two programs (openmx and turbomole) with and without spin-orbit interaction for each case. We used default VPS and PAO for openmx calculations, and our pseudopotential and basis for turbomole. (We also tried our pseudopotential and basis embedded in openmx format, and results were quite close to the default ones).

Both programs gave similar results in case of no so-interaction, but when the latter was enabled, in both programs orbital energies were split, but only in turbomole it resulted in change of electron distribution.
1. We calculated LJ-occupancies and for d-electrons results are:
|D,1.5> 1.60
|D,2.5> 2.40
for openmx-noso, openmx-so and turbomole-noso, and
|D,1.5> 1.74
|D,2.5> 2.26
for turbomole-so
2. We compared spin density (or "magnetization" for turbomole) cube files, and they were of exact cubic symmetry for openmx-noso, openmx-so and turbomole-noso and distorted for turbomole-so.

So, the question is if it is possible to achieve the change of electronic distribution in OpenMX with spin-orbit interaction enabled?

All essential files, including cube files and images are shared at the folder.
dm_ljm.mat file is density matrix, converted to N/L/J/MJ basis.

Best regards,
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Re: Spin-orbit interaction and electron structure in NCDFT ( No.1 )
Date: 2018/01/07 07:48
Name: Daniil


Any information or advices about this case?

Best regards,
Re: Spin-orbit interaction and electron structure in NCDFT ( No.2 )
Date: 2018/01/08 13:36
Name: Chi-Cheng Lee  <>

Hi Daniil,

From a user's point of view, I guess the default energy cutoff is too small to give a noticeable
distorted charge density from the cubic one. The charge density could also not converge very well.
This might not be due to the difference between openmx and turbomole.
Could you try to add the following parameter?

scf.energycutoff 200

and also try to change 200 to 300, 400, or 500 to see if there is any difference in the spin density?
For me, I would also add

Atoms.UnitVectors.Unit Ang
10 0 0
0 10 0
0 0 10

to specify the unit cell size and I will also set k point to 1 1 1, such as

scf.Kgrid 1 1 1

to save time.


Re: Spin-orbit interaction and electron structure in NCDFT ( No.3 )
Date: 2018/01/08 14:43
Name: T. Ozaki


I checked "nb.out" and "nb.sden.cube" stored in "openmx-so", and found that
the charge distribution deviates from the cubic one. It can be seen that the Mulliken
populations violate the cubic symmetry. In addition to this, if you carefully look at
isosurface of the cube file, the distribution looks like tetragonal rather than cubic,
while "nb.sden.cube" stored in "openmx-noso" remains cubic.
Also, please be careful that there is freedom in the distribution due to degeneracy
of the spin-orbit states, which may cause the difference between OpenMX and TURBOMOLE.


Re: Spin-orbit interaction and electron structure in NCDFT ( No.4 )
Date: 2018/01/16 04:52
Name: Daniil

Thank you for answers.

I tried to increase scf.energycutoff, but with only small, if any, effect. Yes, under close study cube files are slightly distorted from cubic symmetry, but much less than in turbomole case.

As for LJ-distribution:
Correct me, if I am wrong, but in first order, SO interaction is proportional to l*s, so that degeneracy between j=l±s states should disappear.
Thus, electrons must redistribute, which can be seen in case of Turbomole calculations: initial non-so distribution is 1.6:2.4 = 4:6, where 4 and 6 are total numbers of j=1.5 and j=2.5 states for D-shell, while under SO interaction j=1.5 states become lower by energy and their total occupation increases to 1.74.

Best regards,

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