Manually entering exchange coupling parameters using the spin package

Hello all

I have a question regarding the exchange parameter inputs. We are currently using the Bethe-Slater function for fitting the exchange parameters. So I wonder can we use some other function like RKKY type or can we manually enter the exchange parameter as a function of distance? In the case of hexagonal systems like Gd, the Bethe-Slater function fits well up to four nearest neighbor interactions (see the attached figure with a cutoff radius of 7 A). I want to include the higher-order interaction terms in the calculation.

Thanks in advance.

Hello @Lokanath ,

In the introduction of your question, I believe you should precise that this is related to the SPIN package and the fitting magnetic Hamiltonians. Otherwise, this might be confusing to people who are not familiar with magnetism (and with the SPIN package).

This question seems to be very specific to your problem and to the associated models. I’m not sure I can help you with this. Overall, you have an optimization problem in front of you: models implemented in a code, and you want them to match a series of data.

At this stage, I assumed you only tried the scripts provided in the examples of the SPIN package. There might be better ways, for example:

  • overlaying two exchange interactions, and trying to fit the parameters (altogether or separately) with a better optimization algorithm,
  • trying other interactions implemented in the SPIN package (biquadratic exchange, Néel interaction, …).

Note that there might not be a perfect solution to your problem. Optimizing potentials can be a difficult task.

Hope this helps,

Thanks, @julient. Let me try with other available magnetic Hamiltonians.
As per your suggestion, I have added the SPIN keyword in the subject line.

Best regards