Core: cubic anisotropy

[Zeleznyj]

As far as I could find, there is currently no support for cubic (4th order) anisotropy.

I can try to implement this myself, however, I'm not sure what exactly would have to be modified. I suppose the main thing is modifying the E_Anisotropy and Gradient_Anisotropy functions within the Hamiltonian_Heisenberg.cpp file and of course the input parsing, however I'm not sure if there is anything else within the code that would need to be changed.

[GPMueller]

This is a good suggestion. I believe we will implement it, but probably not so soon.

I believe you have already figured out how to implement it yourself:

• add the parameter to the constructor of Hamiltonian_Heisenberg in core/include/engine/Hamiltonian_Heisenberg.hpp and core/src/engine/Hamiltonian_Heisenberg.cpp
• add the parameter parsing to Hamiltonian_Heisenberg_from_Config in core/src/io/Configparser.cpp, where the Hamiltonian is constructed
• either add a new functions to Hamiltonian_Heisenberg or simply add the cubic term to the E_Anisotropy and Gradient_Anisotropy functions

[Zeleznyj]

Thanks, I will try to implement this and if I make it work, I will share the code.