[QE-users] Requesting Help With Spin Orbit Coupling Spin-Separated Bands Extraction

[Luiz Gustavo Davanse da Silveira]

Dear Pratyush Manocha,

Now I'm the one who has to apologize about a delayed response.

> Thank you for informing me about the "lsigma" keyword. While it doesn't
> solve my problem of segregating spin-up bands from spin-down ones, it
> gives me the expectation values of the total angular momentum along the
> x, y, and z axes, right?

It gives you the expectation values of the spin operator.

> I tried extracting the data for GaAs, and I noticed from the results that
> often, the expectation values are values other than 0.5, 0, and -0.5;
> does this mean that, at these points, the band has a mix of both spin-up
> and spin-down electrons?

Well, you might find sources that describe it like that, but, as I see it,
in noncollinear calculations each electronic state can have its own spin
quantization axis. Therefore, global spin-up and spin-down states may not
be a good description. Rather, depending on the complexity of your system,
at each k-point of a given band spins may be align in a particular
direction. You could, in principle, determine which direction this is and
define locally what is spin up and spin down, I don't know if it's worth
it, though. Simply put, "lsigma = 1,2,3" gives you the three orthogonal
components of the spin vector. If you take the modulus, the result should
be 0.5 (or close to it).

> Another question I had is: when you say that I can color the bands
> according to the spin values like a fatband plot, do you mean that each
> band would individually be coloured from "colour a" to "colour b" based
> on the spin values at the different k points along the chosen "k-path?"

Exactly. This form of showing the data might not be useful if bands are
degenerate. But if the bands are splitted and spin-polarized you will end
up with a graph showing something similar to spin-up and spin-down bands.

Best regards,

Luiz Gustavo Silveira
Assistant professor, Department of Physics - Federal University of Paraná
Curitiba - Brazil


Em Qui, Março 9, 2023 11:47 pm, Manocha, Pratyush escreveu:
> Dear Professor Luiz,
>
>
> I apologize for my delayed response; I had exams to appear for.
>
>
> Thank you for informing me about the "lsigma" keyword. While it doesn't
> solve my problem of segregating spin-up bands from spin-down ones, it
> gives me the expectation values of the total angular momentum along the
> x, y, and z axes, right?
>
> I tried extracting the data for GaAs, and I noticed from the results that
> often, the expectation values are values other than 0.5, 0, and -0.5;
> does this mean that, at these points, the band has a mix of both spin-up
> and spin-down electrons?
>
> Another question I had is: when you say that I can color the bands
> according to the spin values like a fatband plot, do you mean that each
> band would individually be coloured from "colour a" to "colour b" based
> on the spin values at the different k points along the chosen "k-path?"
>
> Thank you very much for helping me with this!
>
>
> Regards,
> Pratyush Manocha
> Graduate Student | M.S. Electrical & Computer Engineering
> School of Electrical and Computer Engineering
> Georgia Institute of Technology
> ________________________________
> From: Luiz Gustavo Davanse da Silveira <lgsilveira at fisica.ufpr.br>
> Sent: Thursday, February 16, 2023 14:03
> To: Manocha, Pratyush <pmanocha at gatech.edu>
> Cc: users at lists.quantum-espresso.org <users at lists.quantum-espresso.org>
> Subject: Re: [QE-users] Requesting Help With Spin Orbit Coupling
> Spin-Separated Bands Extraction
>
>
> Dear Pratyush Manocha,
>
>
> I believe the spin_component variable doesn't work with noncollinear
> calculations. You can however use the lsigma variable in bands.x input to
> get the spin components at each k-point for every band. Then, for
> instance, you can use this information to color the band plot according
> to spin values (like a fatbands plot).
>
> Best Regards,
>
>
> Luiz Gustavo Silveira
> Assistant professor, Department of Physics - Federal University of Paraná
> Curitiba - Brazil
>
>
> Em Seg, Dezembro 19, 2022 7:22 pm, Manocha, Pratyush escreveu:
>
>> Dear All,
>>
>>
>>
>> I am using QE-7.1 and want to plot the spin-orbit coupled bands for
>> Silicon and later on, GaN. I ran a few simulations for Silicon (with a
>> fully relativistic pseudopotential obtained from PSLibrary 1.0.0) by
>> turning on the "lspinorb" and "noncolin" keywords and specifying a
>> non-zero "starting_magnetization" in the "&system" namecard.  The
>> simulation runs smoothly, however, when I try to extract the bands for
>> just spin-down electrons using "spin_component=2" in the input file
>> given to the bands.x code, it returns the following error: Error in
>> routine punch_bands (1):      incorrect spin_component???.
>>
>> I went through the archive and also tried simulating with various
>> different keyword combinations using "nspin" and "lspinorb", and I found
>>  that "lspinorb" requires non-colinear spin vectors whereas "nspin=2"
>> requires colinear spins, therefore, they would not work simultaneously.
>>  As a result, I can not use the "spin_component" keyword in the bands.x
>>  input file to extract the spin separated bands. So my question is: if
>> I
>> am using "lspinorb=.true." and "noncolin=.true.", is there a way to
>> extract the spin-up and spin-down conduction and valence bands
>> separately?
>>
>> Any help would be appreciated.
>>
>>
>>
>> Regards,
>> Pratyush Manocha
>> Graduate Student | M.S. Electrical & Computer Engineering
>> School of Electrical and Computer Engineering
>> Georgia Institute of Technology
>> [cid:f2b1f8a4-9ef8-4579-9715-844bf6b1658b]
>>
>>
>>
>
>
>