'extra/bond/angle/dihedral/improper/per/atom' and 'extra/special/per/atom' keywords in LAMMPS

Can someone explain the difference between these two keywords? I cannot figure out

One is for storing atoms of a bond/angle/dihedral/improper interaction, the other is for storing excluded neighbors. The latter may not be part of any of the former.

Just check out the output of a regular run with bonded interactions, e.g. here lammps/log.27Nov18.peptide.g++.1 at ceb9466172398e9a20cb510528b4b17f719c7cf2 · lammps/lammps · GitHub

It reports how much space for each of those is being allocated since by default LAMMPS will allocate only the minimum required by a given system.

Could you please explain what “storing excluded neighbors” means?Thanks

Please see the special_bonds command — LAMMPS documentation
and read up about the use of exclusions in molecular force fields your favorite text book on molecular dynamics and force fields.