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Understanding exchange coupling parameter calculation
Date: 2019/09/01 01:35
Name: Jhon W. Gonzalez

Hello OpenMXers!

I'm trying to calculate the exchange coupling parameter J in a CrI3 monolayer using the JX code. (https://arxiv.org/pdf/1809.01388.pdf)
For Cr atoms, I obtain a magnetic moment of +4.2 mB and for I atoms the magnetic moments are about -0.5 mB (mB = Bohr magneton).

Using a k-grid of 9x9x1, I'm finding that the J between Cr-Cr is positive and depending on the basis-set the J value is +3.3 meV (2s2p1d) or +14.3 meV (3s3p3d1f). According to the literature, the value of J for Cr-Cr interaction is about 2.2 meV.
The J for the Cr-I interaction is more consistent, being always around 0.4 meV, regardless the basis-set.

* How can we understand such variation in the value of J only for the Cr-Cr case?

* If J > 0 means an FM interaction, I don't understand why for Cr(+4.2 mB)-I(-0.5 mB) it is also J > 0.

* Which parameters should I adjust to increase the quality/convergence of the calculation with JX?

Thank you very much for your comments!

Best regards,

Jhon W. Gonzalez
Departamento de Fisica
Universidad Tecnica Federico Santa Maria
VALPARAISO - CHILE
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