Some notes on the use of SpaceGroupIrep and vasp2trace for spin orbit coupling and spin polarized calculations.

[hongyi-zhao]

1. In general, we can't do spin orbit coupling and spin polarized calculation simultaneously, as commented here:

The term "spin polarized calculations" assumes that the spatial and spin coordinates in one-electron eigenfunctions are
separable, i.e. each one-electron eigenstate is characterized with definite value of one-electron spin projection, being either
 "state-spin up" or "state-spin down". As we include spin-orbital coupling in the Hamiltonian, it is no longer so. The one-
electron eigenstates will be then the linear combinations of "spin up/down states", being neither "spin up", nor "spin down" 
states, so, it would make no sense to tell about "spin polarization", - in general.

The following are some relevant comments/discussions:

• ProcarPy:
  
• PROCAR:
  
• Please also refer to the relevant discussion here.

2. vasp2trace has different versions for spin polarized and non spin polarized calculations:

For the meaning of the parameter, see here:

    ISPIN=1: non spin polarized calculations are performed.
    ISPIN=2: spin polarized calculations (collinear) are performed.

3. The convTraceToBC function in SpaceGroupIrep uses different argument list for SOC and non-SOC cases:

$ rg -A4 convTraceToBC::
SpaceGroupIrep.wl
237:convTraceToBC::usage="convTraceToBC[sgno,traceData,P,p0,stdR]  converts traceData from non-BC standard to BC "<>
238-   "standard for getBandRep to determinate little group ireps. P, p0, and stdR are respectively "<>
239-   "dataset['transformation_matrix'], dataset['origin_shift'] and dataset['std_rotation_matrix'] "<>
240-   "from spglib acting on the initial cell. For non-SOC case stdR is not needed but for SOC case "<>
241-   "stdR has to be given.";

Here are some related comments.

[goodluck1982]

2. vasp2trace has different versions for spin polarized and non spin polarized calculations:

getBandRep works for the trace.txt (or trace_up.txt and trace_dn.txt) file generated by all these versions.

3. The convTraceToBC function in SpaceGroupIrep uses different argument options for SOC and non-SOC cases:

Strictly speaking, the function convTraceToBC should be called with the same number of arguments for both SOC and non-SOC. However, when called in noo-SOC case, the argument stdR can be anything and do not affect the results. That it to say, stdR has to exist but not work in this case.

[hongyi-zhao]

However, when called in noo-SOC case, the argument stdR can be anything and do not affect the results. That it to say, stdR has to exist but not work in this case.

Do you mean that the following usage is sufficient in non-soc situation?

convTraceToBC[sgno, traceData, P, p, ""]

[goodluck1982]

Yes.

[goodluck1982]

That it to say, stdR has to exist but not work in this case.

Sorry, I forgot I had defined the function overload:

convTraceToBC[sgno_Integer,traceData_,P_,p0_]:=convTraceToBC[sgno,traceData,P,p0,IdentityMatrix[3]]
convTraceToBC[sgno_Integer,traceData_,P_,p0_,stdR_]:=......

So, the stdR argument can be omitted. If omitted, it's default value is just the identity matrix.

[hongyi-zhao]

So, in non-soc situation, the following is enough:

convTraceToBC[sgno, traceData, P, p]

The function called above will be converted to the following form before execution:

convTraceToBC[sgno,traceData,P,p0,IdentityMatrix[3]]

[goodluck1982]

You are right.