[lammps-users] Errors making LAMMPS-- libcore.a, etc "not of required architecture"?

The basic idea is simple. The Reax lib (in lib/reax) is Fortran
code, which you build into a libreax.a file. When you build
LAMMPS you link to that library using a C++ compiler. Since
LAMMPS is C++, you usually have to specify additional libs
to link to a Fortran library. The src/MAKE/Makefile.foo file
is where you specify those (in the Reax section). Which libs
you need to list depends on your compilers and your box,
which is not a LAMMPS issue, but a compiler issue for
any C++ to Fortran linking. Your compiler manuals should
explain how to do this. The -lifcore that appears in some
Makefile.foo files, is one such lib used when using Intel compilers.