LAMMPS ..../examples/RDX/param.qeq

Hi All,
I am very new to LAMMPS. I have been going through some examples and found param.qeq in RDX example. I have been wondering about param.qeq file. What do we need the file for?

I would appreciate your help.

Well, first of all, all relevant details about this file are in the documentation. Please just have a closer look. It will tell you, though, that you (mostly) don’t need it.

To understand why this file is used, you need to know a bit about the history of the ReaxFF package in LAMMPS. It started as a standalone C code called PuReMD (which still exists) and was then adapted to be called from within LAMMPS with the intent to replace an older, less flexible ReaxFF implementation written in Fortran. Over the years, the integration into LAMMPS has become tighter and the code was refactored multiple times to get rid of parts not used by LAMMPS and to more closely follow LAMMPS’ programming conventions.

The parameters in the param.qeq file also exist in the ReaxFF potential file, but those were initially not accessible to fix qeq/reaxff, so the option to read them from a separate file was used. Some time later, a mechanism to query styles for internal data was added to LAMMPS and in combination with a few corresponding changes to fix qeq/reaxff the use of the parameter file became (mostly) obsolete, because the same information could now be obtained from the reaxff pair style. The interface to read a param.qeq file now exists (mostly) for backward compatibility with old inputs.

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@akohlmey Thank you for clarifying.