License: GPLv2 or GPLv3?

Dear LAMMPS developers,

I have a question regarding the GPL version that should/can be used for
modifications to LAMMPS. This would, for example, be relevant for people
who implemented a new potential/algorithm and want to upload a modified
version of LAMMPS as supporting data for their publication.

From the LICENSE file I can tell that LAMMPS is shipped with the GPLv2

which is, in general, not compatible with the GPLv3 by itself. However,
in the LICENSE file there is a sentence saying:

"If the Program does not specify a version number of this License, you
may choose any version ever published by the Free Software Foundation."

In most of the source files, e.g. lammps.cpp, you don't explicitly refer
to GPLv2. However, you also don't say anything along the lines of '...
any later version'. In some files, e.g. USER-REAXC/reaxc_bonds.h, you
refer to GPLv2 explicitly but with the addition 'or (at your option) any
later version'.

I would appreciate if someone from the developer team could comment on
this to clarify whether releasing a modified version of LAMMPS under the
GPLv3 is OK.


I think you are asking about new files that you want to

release (either on your own or contributed to LAMMPS?).

Either way I think it is fine to tag them as GPLv2

or GPLv3.