Dear Wang,

if you look at the PWscf user guide, how to use the noncolin flag is quite well 
explained:

“The following input variables are relevant for noncollinear and spin-orbit 
calculations:

noncolin
lspinorb
starting magnetization (one for each type of atoms)

To make a spin-orbit calculation noncolin must be true. If starting 
magnetization is set to zero (or not given) the code makes a spin-orbit 
calculation without spin magnetization (it assumes that time reversal symmetry 
holds and it does not calculate the magnetization). The states are still 
two-component spinors but the total magnetization is zero.

If starting magnetization is different from zero, it makes a noncollinear spin 
polarized calculation with spin-orbit interaction. The final spin magnetization 
might be zero or different from zero depending on the system. Note that the 
code will look only for symmetries that leave the starting magnetization 
unchanged.

Furthermore to make a spin-orbit calculation you must use fully relativistic 
pseudopotentials at least for the atoms in which you think that spin-orbit 
interaction is large. If all the pseudopotentials are scalar relativistic the 
calculation becomes equivalent to a noncollinear calculation without spin 
orbit. (Andrea Dal Corso, 2007-07-27) See Example 06 for noncollinear 
magnetism, Example 07 (and references quoted therein) for spin-orbit 
interactions.”

If I choose scalar-relativistic pseudopotentials, does this mean nonlinear 
calculation will be included automatically?

No. Then you must set the noncolin flag to .true. (the default is .false.).

HTH


Antimo Marrazzo
Doctoral Assistant
EPFL STI IMX THEOS
ME-D2 1019 (Bâtiment ME)
Station 9
CH-1015 Lausanne (Switzerland)

Il giorno 04 mar 2016, alle ore 00:01, Mingchao Wang 
<[email protected]<mailto:[email protected]>> ha scritto:

Dear All,

I calculated band structures of hybrid perovskite CH3NH3PbI3. I chose 
non-relativistic pseudopotentials for H, C, N elements, and scalar-relativistic 
pseudopotentials for Pb and I elements. In this case, which value of noncolin 
should I set, noncolin =.false or noncolin =.true?

If I choose scalar-relativistic pseudopotentials, does this mean nonlinear 
calculation will be included automatically?

Best wishes,

MC
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