How to switch the direction of the quantization axis of spin from z axis to x or y axis

[fangrh]

Details

I have a trivial question. When calculating two-dimensional materials, the normal vector should not set to the z axis to improve performance. When setting the spin, the quantization axis defaults to the z direction. But in most cases, in 2D material, the quantization axis is oriented to the normal vector of the 2D materials. I would like to ask, how to set the default quantization axis to the x or y axes?

Have you read FAQ on the online manual http://abacus.deepmodeling.com/en/latest/community/faq.html

• [X] Yes, I have read the FAQ part on online manual.

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[QuantumMisaka]

In my practice in Fe5C2 (510) surface, this problem does NOT EXIST, the TMAG and AMAG are both 143 - 145 and 154 - 156 no matter I set normal vector to y-axis or z-axis. I am using 405 function of ATOMKIT, which can switch the x/y/z lattice vector in cell. and when normal vector is set along y-vector, the MPI parallel function will be accelerated.

In my opinion, the nspin=2 does NOT mean that the spin axis is fixed along z-direction, but means that spin-up and spin-down is collinear, and the freedom of spin is 2.

[fangrh]

That's quite reasonable. The distinct spin axis orientations correspond to different state bases, which will not influence the result(in most cases ? I am not sure.).

However, I'm curious about the impact when applying a magnetic field. It seems that the Hamiltonian might become off-diagonal if the spin axis is not parallel with magnetic field, refers to page 175 of Doctor Warren's thesis. Could this off-diagonal feature potentially influence the performance or the results of the calculations?

I apologize for the numerous questions; I'm relatively new to DFT, and I appreciate your patience.

[QuantumMisaka]

@mohanchen Any comments ?

[mohanchen]

I may not be familiar with this isseu, @dyzheng do you have comments?