MEAM: the Z parameter

Hi all,

this is a question to anyone using MEAM potentials in LAMMPS about a change I'm considering for MEAM/C and I'd like your input first.

The library lines contain a reference structure (lat) as well as the number of nearest neighbors in the reference structure (z). It is therefore possible to enter arbitrary combinations of reference structure and coordination numbers. In my opinion, this is not very useful and can obviously lead to problems if one is not careful to enter meaningful values (this just happened to me, hence the idea).

My question is: is anyone aware of a potential that uses a "wrong" value, for example to fit some special property?

In code, we already have a table for getting Z from the structure identifier, and in fact this is used in many places of the code already - but not all, some (8 of 28) use the user-provided value. Following the principle of least surprise, I would always use the structure value, remove the ability to specify a different value, and simply check the input for correctness and warn if it is not, but otherwise ignore it. The check will be implemented in either case, but I don't want to break someone's application without asking first.