I am using the pair_style reax/c force field , and I have some questions about the force field file ffield.reax.**
what is the units used in the ffield.reax** ? how could I know the units for energy , length … used in ffield.reax.** ? is there any string labels or numbers indicate the units system used in the file?
If I get a force field file from the literatures , and the format of the file looks like the one in the examples from lammps. what should I concern when I use the obtained file? how should I make sure 1. the units in the file is proper for the code in lammps, and 2. datas in the file is exactly the datas required by the code in lammps?
I know making a test calcultion is a method for this, and I want to know whether other knowledge I am supposed to know (e.g different versions of reactive force field formula format which are not compatible with each other) ?
I am using the pair_style reax/c force field , and I have some
questions about the force field file ffield.reax.**
what is the units used in the ffield.reax** ? how could I know the
units for energy , length ... used in ffield.reax.** ? is there any
string labels or numbers indicate the units system used in the file?
units used in ReaxFF force field files can be identified by reading its
papers and the ReaxFF manual (available online or from Prof. Adri van
Duin's website).
If I get a force field file from the literatures , and the format
of the file looks like the one in the examples from lammps. what should I
concern when I use the obtained file? how should I make sure 1. the units
in the file is proper for the code in lammps, and 2. datas in the file is
exactly the datas required by the code in lammps?
LAMMPS reads published ReaxFF force field files without a problem - you
usually don't have to worry about the format or the units. Just make sure
you can somehow reproduce the published results then you know you have the
correct force field file.
I will also add this comment (Ray can clarify if I’m wrong).
From the Reax/C doc page:
The ReaxFF potential files provided with LAMMPS in the potentials directory are 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.
The LAMMPS setting for its “units” command in your input
script needs to be consistent with the force field file as well.
If LAMMPS is using “real” units then any parameter in
that file for energy, distance, etc, should be consistent
with what LAMMPS expects for real units, i.e. Angstroms
Kcal/mole, etc.