[Pw_forum] spin splitting

[vtmtrinh at caltech.edu]

Thanks a lot for your help.

Also, I have another question.  How is the spin-orbit implemented in QE,
i.e. is there any approximation.  In other words, could you give me the
ref that QE is based on (if any).  I am looking for the part of the code
that ralted to the spin-orbit, but so far, I still could not locate it.  I
appreciate if you could let me know.

Best,

MyTrinh

>
>
> vtmtrinh at caltech.edu wrote:
>> Hi Gabriele,
>>
>> Thanks for your reply. I am sorry for the unclear question.
>> The question is to calculate the splitting between the spin up and spin
>> down states in the conduction band (CB) of Si. For equlibrium Si bulk,
>> there should be no spin splitting. Therefore, the splitting can be
>> induced
>> by moving the atoms a long phonon modes. The spin splitting is probably
>> of
>> the order ~1e-7eV.
>>
>> Yes, you are right.  I need to set nspin=2.  Since I also need to
>> include
>> the spin-orbit coupling in this calculation, I have to use
>> noncolinear=.true.
>
> Now the situation is much more clear :-)
>
>
>>
>> I run a calculation yesterday, in which I set lspinorb=.true. and
>> noncolinear=.true. By setting this I think that spin-polarized
>> calculation
>> was aslo done.  However, in the output, I don't see the eigen values for
>> spin up and spin down, but only one (like for the non-polarization
>> case).
>
> You're right, in a noncolinear calculation you don't see SPIN UP and SPIN
> DOWN bands as in
> a LSD calculation.
> Anyway, as you also noticed, the number of bands is doubled when you set
> noncolin=.true.
> If you don't include SO coupling, you should get (for each band of the non
> spin-polarized
> calculation) a spin up and a spin down band which coincide with those
> obtained with a
> collinear LSD calculation (i.e. with noncolin=.false., nspin=2). Also the
> final total
> magnetization should be the same (you can check from the output).
> You can plot the bands (for instance using bands.x and then plotband.x)
> and compare the
> splittings.
> When you include SO the situation is more complicated (you should label
> your bands with
> the irreps of the (magnetic) double group of the system), but in principle
> more close to
> reality.
> You can plot bands also in this case and see what changes and how much
> (tyr lsym=.true.
> when running bands: it can label bands according to the irreps and it may
> be very useful).
> The SO splitting would be small, though. In the Si atom the SO splitting
> of 3p electrons
> should be of the order of few mRy (which is only slightly larger than the
> error from PPs,
> so be careful...), and in the bulk they are usually lower.
>
>
> Cheers,
>
> GS
>
>
>> I am not sure if I did not set the right parameters.  Attached is my
>> input.  Could you let me know what wrong with it.
>>
>> Thanks,
>>
>> MyTrinh
>>
> --
>
>
> o ------------------------------------------------ o
> | Gabriele Sclauzero, PhD Student                  |
> | c/o:   SISSA & CNR-INFM Democritos,              |
> |        via Beirut 2-4, 34014 Trieste (Italy)     |
> | email: sclauzer at sissa.it                         |
> | phone: +39 040 3787 511                          |
> | skype: gurlonotturno                             |
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