Lammps dipole/chunk with reaxff


I am now using the reaxff force field and would like to calculate the dipole moment of each molecule in my system. I am now using, compute chunk/atom molecule and compute dipole/chunk to achieve this.

I am wondering, within a molecule, if some bonds are broken (e.g., C-H bond), H atoms leave the molecule and become H2, will these H atoms still be considered when computing the dipole moment of this molecule.

Thank you very much.



Compute chunk/atom molecule will partition the system based on the molecule ID. That is an input that you provide and that doesn’t change over the course of a simulation (unless you change it somehow).

If you want to know the partitioning of atoms into molecules based on the ReaxFF bond order property (which is how ReaxFF decides whether atoms are bonded or not), then you need to use fix reaxff/species and use the per-atom output of that fix as input to compute chunk/atom, so it will change the partitioning of the system into chunks in the way how ReaxFF “sees” it. Those chunks will then be processed by compute dipole/chunk accordingly.

Thanks Axel, that makes sense. I could get my expected output from that.