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Spi-orbit coupling
Date: 2021/01/13 19:40
Name: Artem Pulkin   <gpulkin@gmail.com>

What is the difference between setting

scf.spinpolarization off
scf.spinorbit.coupling off

and specifying zeros in scf.so.factor? On the Bi2Se3 example I learned that the first option produces a substantially larger band gap than the second one.
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Re: Spi-orbit coupling ( No.1 )
Date: 2021/08/01 11:48
Name: T. Ozaki

Hi,

The case:
scf.spinpolarization off
scf.spinorbit.coupling off

corresponds to the collinear spin-unpolarized calculation with scalar relativistic pseudopotentials
generated with taking account of the j-degeneracy as

V_l = ( (l+1)*V_{l+1/2} + l*V_{l-1/2})/(2*l+1)

On the other hand, the case:
scf.spinpolarization NC
scf.spinorbit.coupling on
specifying zeros in scf.so.factor

corresponds to the non-collinear calculation with zero spin-orbit coupling, where the pseudpotentials
are generated by

sum = (V_{l+1/2} + V_{l-1/2})/2
dif = (V_{l+1/2} - V_{l-1/2})/2

V'_{l+1/2} = sum + scf.so.factor * dif
V'_{l-1/2} = sum - scf.so.factor * dif


Therefore, if a system is non-magnetic, the difference can be attributed to how to generate the scalar
relativistic pseudopotentials.

These manipulation can be confirmed around lines 902-925 of SetPara_DFT.c.


Regards,

TO
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