need to copy maxspecial and "extra" data to do a proper recreation

  atom->dihedral_per_atom = old->dihedral_per_atom;

  atom->improper_per_atom = old->improper_per_atom;

  atom->extra_bond_per_atom = old->extra_bond_per_atom;

  atom->extra_angle_per_atom = old->extra_angle_per_atom;

  atom->extra_dihedral_per_atom = old->extra_dihedral_per_atom;

  atom->extra_improper_per_atom = old->extra_improper_per_atom;

  atom->maxspecial = old->maxspecial;

  // store old simulation box

  int triclinic = domain->triclinic;