Exchanging Molecules with ReaxFF and GCMC

Greetings Lammpsters!
I have another question for LAMMPS and ReaxFF experts: is it possible to use fix gcmc and pair_style reax/c together to exchange molecules?

The reason I ask this is because in using ReaxFF molecules are not well defined, but can be inferred based on the bond order structure. So my intuition tells me it might not be possible, but I wanted to appeal to the experience of community first before I jump to conclusions.

Josh Deetz
PhD Candidate Student
Chemical Engineering
University of California, Davis
ยง 408-242-5523

It is not possible currently in the following ways:

1. As you said, ReaxFF does not pre-define molecules, so the fix gcmc
does not know what collection of atoms to apply MC operations
(insertion, deletion, translation and rotation) to.

2. ReaxFF is reactive, so that the molecule pre-defined as the
template exchange molecule may not exist in later time. This can be
solved by making ReaxFF non-reactive.

3. The current implementation of fix gcmc, as described in the doc
page, includes only pair-wise interactions so that many body
potentials cannot be used.

Unless you make significant modifications to fix gcmc and make a
non-reactive ReaxFF (by turning off bond-order calculations), it is
not possible to use fix gcmc with ReaxFF.