Dear Axel,
thank you for your reply. I tried to use ‘fix external’ but I’m having troubles passing the pointer for the callback function (pf/callback) or for the array (pf/array) to lammps.
I could not find instructions in the manual and the only examples with ‘fix external’ do this from C++.
For instance, the example examples/COUPLE/lammps_quest uses the C++ lines: