Qeq/reaxff or qeq/reax

The documentation for fix qeq/reaxff - fix qeq/reaxff command — LAMMPS documentation shows the command as

fix ID group-ID qeq/reaxff Nevery cutlo cuthi tolerance params args

but this results in an error. Should this be

fix ID group-ID qeq/reax Nevery cutlo cuthi tolerance params args

or am I mistaken?

Thank you

What LAMMPS version are you using? The online documentation always reflect the latest patch release version. Sometimes commands get renamed or altered, so you must consult the version of the documentation that matches the version of LAMMPS you are using. That documentation may use different names than the latest patch (or stable) release.

In the case of fix qeq/reaxff the “old” name of the command is indeed fix qeq/reax (which is somewhat inconsistent and that is why we changed it when we refactored and consolidated the ReaxFF implementation during the last development cycle).

I am using 3Mar2020, that makes sense! Thank you.

Do you know of 3Mar2020 has the ability to get reaxff parameters from the forcefield file (by specifying reaxff instead of a param file)?

Probably yes, but the only way to know for certain is to check the corresponding documentation.
If you download a tarball from lammps.org, a PDF should be included. Otherwise, you can go to the doc folder of the source and build the html documentation locally with “make html” and then load the corresponding html file in the html folder into your web browse. Details about the procedure and prerequisites are, of course, in the manual.