About the ffield.reax file

Dear all,

I have found a ffield.reax file from the supporting information of one literature. I have carefully checked and compared the format of this ffield.reax file with the other ffield.reax.label files in src/Potential. And the only difference is the number of general parameters is 40. However, I have checked all the ffield.reax.label files in the src/Potential file, and all the general parameters are 39. I am not sure that the present reaxff force field in Lammps supports this additional parameter and how the Lammps will deal with it. I apologize if this problem is trivial. Thanks for your time and kind help!

My questions are as follows:

  1. Can I use this ffield.reax file like other ffield.reax.label files from the src/Potential file. I have checked the file format; the only difference is the number of general parameters.

  2. And how the Lammps would deal with this 40th general parameter? Should I delete this line or leave it alone (If the Lammps will not read in this parameter)?
    The 40th general parameter is “2.000 !triple bond on/off (0 for CO, 1 for CO and N2 , 2 for all)”.
    It seems like this parameter is a trigger influencing the formation of some molecules.

  3. If I use this new ffield.reax file. Can I use the fix qeq/reaxff with params = reaxff? This ffield.reax file is developed by Dr. Adri van Duin’s group, I think the charge equilibration method used is probably the same as the ffield.reax.cho in src/Potential file. The chiEEM, etaEEM and gamma in this ffield.reax file has changed slightly compared to the ffield.reax.cho in the src/Potential file.

  4. In the src/Example/qeq and reax folder, I have found all the input scripts using reaxff as the force field has also used the params = filename (such as param.qeq.reax) in fix qeq/… command. Is this just to provide a template for params file?

I really appreciate your time and help!

Best regards,
Shusen Guo

Technically, yes. LAMMPS will read and store the additional global parameter internally, but nothing will use it.

You don’t have to edit the file.

Yes.

The separate parameter file for qeq/reaxff is a LAMMPS invention. It was only later changed, when a method was added to LAMMPS to retrieve the parameters from the pair style. The base of the REAXFF pair style was a standalone C code (It still exists and is maintained as PuReMD)
which was revised and refactored for use in LAMMPS multiple times.

Most of the examples predate the option to retrieve atom parameters from the pair style.

Really appreciate for your explanation and help!
This is really helpful!

Best regards,
Shusen Guo