delete update;

  delete neighbor;

  delete comm;

  delete domain;

  delete force;

  delete group;

  delete output;

  delete modify;          // modify must come after output, force, update

                          //   since they delete fixes

  delete domain;          // domain must come after modify

                          //   since fix destructors access domain

  delete atom;            // atom must come after modify, neighbor

                          //   since fixes delete callbacks in atom

  delete timer;