About the ffield.reax file

[Shusen_Guo1]

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

[akohlmey]

@Shusen_Guo1

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.

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

@Shusen_Guo1

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)”.

You don’t have to edit the file.

@Shusen_Guo1

If I use this new ffield.reax file. Can I use the fix qeq/reaxff with params = reaxff?

Yes.

@Shusen_Guo1

I think the charge equilibration method used is probably the same as the ffield.reax.cho in src/Potential file.

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.

@Shusen_Guo1

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?

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

[Shusen_Guo1]

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

Best regards,
Shusen Guo