"Custom" use of SLATM and mbtypes

[puckvg]

Hello,

I would like to use your nice all-python SLATM function. I notice that the typical use case in the examples is to have a full dataset pre-defined, which sets the mbtypes as combinations of elements in each individual molecule. What about if I instead wanted to specify only the nuclear charges I expect to see up-front, e.g. unique_elements=[1,6] , such that I can generate mbtypes once at the beginning and then construct new SLATM representations "on the fly" for new molecules with elements falling into those pre-defined?
I tried just giving one example molecule with the above unique elements, but the three-body terms are empty, presumably since there are only two atoms in my pseudo-molecule. What is the best way to set up mbtypes to cover all use cases? Set up a pseudo-molecule with at least three of each element I want to consider?

Thanks in advance!