Units of spin texture in kSpin output

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Units of spin texture in kSpin output

Date: 2026/03/12 17:39
Name: Xinliang Huang <xilhuang@foxmail.com>: Dear OpenMX developers,

I have a question regarding the units of spin texture obtained from the kSpin utility.

I calculated the spin texture using OpenMX (with non-collinear DFT + SOC) and the resulting spin components (from the Pxyz_* files) range from approximately -0.075 to 0.075.

However, when I construct a tight-binding model from the same OpenMX calculation using Wannier90, and then compute the spin texture via the expectation value <ψ|σ|ψ>, the resulting values range from -1 to 1.

Could someone clarify the following:

What are the units of the spin components (Sx, Sy, Sz) in the Pxyz_* files generated by kSpin?

Why is there such a large numerical difference (a factor of roughly 13) between the OpenMX output and the Wannier90-based tight-binding model? Is this due to a difference in normalization conventions, unit systems, or post-processing steps?

Any insight would be greatly appreciated. Thank you in advance!

Best regards,
Xinliang Huang

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Re: Units of spin texture in kSpin output ( No.1 )

Date: 2026/03/13 01:15
Name: Naoya Yamaguchi

Hi,

It is basically as described in the manual:
https://www.openmx-square.org/openmx_man3.9/node176.html

However, the values for the following keywords are set to scale the output values for visualization purposes. If any of these are not set to 1, the size will differ from what would be output otherwise.

> MulP.Vec.Scale
> Specify a scale to draw vectors expressing the spin texture. For example, values '0.1 0.2 0.3' specifies the scale as follows: 0.1 for x-axis, 0.2 for y-axis, 0.3 for > z-axis. This keyword affects only 'XXXXX.Pxyz_YY' (XXXXX = the value for the keyword 'Filename.outdata'; YY = the band index). The default is '1.0 1.0 1.0'.

Regards,
Naoya Yamaguchi

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