# How can I obtain seperate spin-up and spin-down bands while considering Spin Orbit Coupling in Quantum ESPRESSO?

I have been studying a magnetic material with SoC taken into consideration. The main aim was to obtain the band structure.

when I use spin_component = 1 in the bands.x input file, I get a bands.dat file containing the bands for the spinup configuration.

But on using spin_component = 2, it throws the following error.

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Error in routine punch_bands (1):
incorrect spin_component
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


I found this discussion on the pw-Forum, in which it was stated that:

In the spin-orbit case starting with zero starting_magnetization on all atoms imposes time reversal symmetry. The magnetization is never calculated and kept zero (the internal variable domag is .FALSE.).

So is there a way to obtain the spin-polarized bandstructure in Quantum ESPRESSO whilst taking into consideration Spin-Orbit Coupling?

• 'Spin-polarization' and SOC don't go along with each other. The wave function becomes a spinor when you include spin-orbit coupling. So there's no meaning of 'majority' or 'minority' carrier, since the spins can point in different directions. – Xivi76 Feb 5 at 21:35

## 1 Answer

• If you are considering SOC, which means the noncolinear calculations are performed. I assume that the eigenstate of the Kohn-Sham equation is labeled by $$|atom, k, orbital, spin \rangle$$. To obtain a spin-polarized band structure, you should do a fat band analysis with the consideration of the different spin components:

• $$\langle atom, k, orbital, spin|s_x \rangle$$ (plus=left;minusright)
• $$\langle atom, k, orbital, spin|s_y \rangle$$ (plus=front;minus=back)
• $$\langle atom, k, orbital, spin|s_z \rangle$$ (plus=up;minus=down)
• You may take a look at my answer for this post: Properties that can be deduced from Band structure and DOS

• For your question, the key problem is to output band structure with projection to spin. The same function is realized with LORBIT=11 in VASP.