Dear Jiaqi,

To see these results it is not needed to switch on l_noco. Leave it set as "F". If the l_noco switch is set to "T", the calculationSetup/coreElectrons/@ctail switch also has to be set to "F". That is what the error message tells you.

You actually have to do the following things to see the spin-polarization in the band structure:

1. In the inpgen input you have to select a spin-quantization axis, for which you actually expect to see the effect. For the BiTeCl example you wouldn't see anything interesting if this is the z-axis, as it is set in the tutorial. For that case it would be more reasonable to set both angles to 1.570796327=0.5*Pi, i.e., the y-axis.
2. In the fleur input file you have to set jspins to 2, just as you did.
3. When you execute fleur, you obtain a warning because you run a spin-polarized fleur calculation without having a magnetic moment in the setup. Just ignore that warning by invoking fleur with the command-line switch -warn_only.

With the new inpgen input the input generator will find less symmetries in the system, which means that you get more k-points for the calculation. Also in the fleur calculation you have to set up and solve the problem for both spins. These two aspects imply that the calculation will take much longer than in a non-spinpolarized calculation.

I attach for the BiTeCl example inputs for the self-consistent field calculation (inp1.xml) and the band structure calculation (inp2.xml) and a slightly modified python script from the fleur website, adapted to visualize the respective effect (plotBands.py). The attached image bandstructure.png shows the visualization you obtain from this. In cases of degenerate bands it may happen that there are sudden color-changes, because the other band comes to the foreground.

Please note that the band structure plot follows a path from -M over gamma to +M, but both, -M and +M, are denoted as M in the plot.

I hope this clarifies how to obtain the visualization you want to have.

Please also note that this visualization is only possible on the basis of the banddos.hdf file, e.g., with the script above. The association of the states with the two spins is encoded in weights. These are not available for the gnuplot script, which is also often used to plot band structures.