Adjust l_max

[DavidW99]

Dear ACE developer,

Do you know how to specify the l_max using ACEpotentials.jl. I could not find any related information in https://github.com/ACEsuit/ACEpotentials.jl/discussions/new?category=q-a.

Thank you!

[cortner]

We don't specify lmax and nmax but we specify the total degree of the approximating polynomial. The tutorials in the docs show how to do that. If you want to change the relative importance of the n-channels and the l-channels then you can do that using the wL keyword argument. E.g.,

model = acemodel(elements = [:Si,],
                 order = 3,
                 totaldegree = 10,
                 wL = 1.0,        # default is 1.5 
                 rcut = 5.0)

lowering wL increases the degree in l while increasing wL decreases it.

One can of course make more fine-tuned choices, including using a max-degree, but this requires engaging with the code at a much lower level.