I have run into the following error with fix bond/react Fix bond/react: Rmax cutoff is longer than pairwise cutoff. The reason the documentation gives is that “This is not allowed because bond creation is done using the pairwise neighbor list.“ If this is true, shouldn’t the error only be flagged if Rmax cutoff is longer than the neighbor cutoff distance (pairwise cutoff + skin)? It would be very helpful for me and a simulation I am trying to run to be able to still use this fix when Rmax is greater than the pairwise cutoff but smaller than the neighbor cutoff.
Let me know if I am missing something as to why this would not be safe. I understand it is a strange simulation setup to allow atoms to react when they are not even interacting, but I don’t see why it should be completely prevented by this error.
I cannot comment on fix bond/react, but from the perspective of the LAMMPS core code itself it is straightforward. It is incorrect to “abuse” the nighbor list skin to extend the neighbor list cutoff. the purpose of the skin distance is to facilitate less frequent neighbor list updates (at the expense of having longer lists and thus longer loops). The correct way to have a longer cutoff for a “consumer” of a neighbor list that is different from the pairwise neighbor list, is to submit an explicit neighbor list request (see e.g. compute rdf) with a custom cutoff.
@arosario As Axel mentioned, I believe that including the skin distance could cause inconsistent behavior. Note that there are tricks to increase the overall pairwise cutoff without increasing it for particular interactions (although I do not understand why that design choice is necessary). Please let us know if you were able to solve the issue.
Thank you both for responding and for your help. I could not find a different way around it, so I ended up modifying the source code to fit my needs and its running smoothly with the modifications. Cheers!