[lammps-users] units in ffield.reax file

Dear LAMMPS developers,

I would like to ask about units used in ffield.reax file. The documentantion says you use real units. Do they differ somehow from those used in Adri van Duin’s articles? I see some values are the same but other differ much (sometimes even their sign is opposite (e.g. heat increment)). I have also noted (may be I’m wrong) that some energy values seem to be in eV (chiEEM, etaEEM, gammaEEM) although real units use kcal/mole for energy.

I’m asking all this, because I want to take parameters for magnesium and hydrogen from van Duin’s article.

I'll let Aidan answer this. I'm pretty certain the ffield.reax is
all real units.


This is what the documentation says about LAMMPS units and ReaxFF:

"The ffield.reax potential file provided with LAMMPS in the potentials
directory is parameterized for real units. You can use the ReaxFF potential
with any LAMMPS units, but you would need to create your own potential file
with coefficients listed in the appropriate units if your simulation doesn't
use "real" units. This would be somewhat tricky, so contact the LAMMPS
authors if you wish to do this.

The key phrase is "parameterized for real units." This implies that in order
for LAMMPS to generate correct forces and eergies, the units style msut be
set to:

units real

This is not meant to imply anything about the units of the quantities
specified in ffield.reax.