[Pw_forum] noncolin variable for scalar relativistic pseudopotentials

[BARRETEAU Cyrille]

You can use noncolin=true in two cases:

- If you expect that the magnetic configuration of your system is non collinear. In that case you don't need to have a relativistic pseudo. This situation can occur when you have magnetic frustration in your system.

- when you want to include spin-orbit coupling and look at quantities like the magnetic anisotropy.
In that case your need a relativistic pseudo.

But if you want to do standard collinear spin polarized calculation just use noncolin=false (default value)

Cyrille

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Cyrille Barreteau
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________________________________
De : pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] de la part de Lorenzo Paulatto [lorenzo.paulatto at impmc.upmc.fr]
Envoyé : vendredi 4 mars 2016 09:40
À : PWSCF Forum
Objet : Re: [Pw_forum] noncolin variable for scalar relativistic pseudopotentials


You can use either, but you won't get much benefit from noncolin=.true. if you don't use full relativistic pseudos. Also, noncolinear calculations are more expensive, and some features are not implemented in this case.

On 4 Mar 2016 3:32 a.m., "Mingchao Wang" <wmc1406 at gmail.com<mailto:wmc1406 at gmail.com>> wrote:
Dear Dr. Clavijo,

Thank you for your helpful information. My concern is about the setting of noncolin variable. My question is: If I use scalar-relativistic pseudopotentials for all atoms of CH3NH3PbI3, should I use noncolin=.TRUE or noncolin=.FALSE? Now I am not quite whether scalar-relativistic pseudopotentials directly include the nonlinear calculation.

Regards,

MC Wang

On Thu, Mar 3, 2016 at 8:42 PM, Josue Itsman Clavijo Penagos <jiclavijop at unal.edu.co<mailto:jiclavijop at unal.edu.co>> wrote:
Dear Mingchao Wang, as far as i know, the best case is to use Pseudopotentials of the same kind for all atoms, and preferably full-relativistic, so the spin-orbit coupling can be accurately taken into account, since it its known that Eg calculated without relativistic spin-orbit coupling is , although not very different that the no-relativistic calculated one due to cancelling over- and under- estimation issues in non-relativistic pseudopotentials, not a good obtained one. Long words short: you're getting a Eg value from a not so much physically accurate calculation framework.

On the other hand, you not need to use H atoms to calculate Band Structure, since their contribution is only in the deep levels of valence and conduction bands (not near the band gap), unless you are into studying deep band structure actually.

Finalliy, I think that noncolin=true is a must for spin-orbit calculations in pw.x , but i'm not 100% sure if that's true for an hybrid inorganic-organic system such as a CH3NH3PbI3 unit cell crystal at any temperature and crystal system of those this material can form.

Anyway, Would you mind to put your pw input file, so i can compare my calculations with yours, since i'm currently working on the same system? that would be very very helpful to me and for others fellows in the forum and all would help you more and better, also.

Best regards,

Josué Clavijo, PhD.
Assistant Professor
Universidad Nacional de Colombia
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