anchor.diff:  
     integer, dimension(N_species) :: n_solvent
     type(h5md_element_t) :: n_solvent_el
  +
  +  integer, parameter :: block_length = 8
  +  integer :: n_blocks
  +  type(correlator_t) :: msd, oacf
  +  integer(HID_T) :: correlator_group, group
   
     type(histogram_t) :: z_hist
     type(h5md_element_t) :: z_hist_el
  
positive.code:   write(*,*) ''
  
    write(*,*) 'n extra sorting', n_extra_sorting
  
    call solvent_io%position%append(solvent%pos)
    call solvent_io%velocity%append(solvent%vel)
  
negative.code:   type(thermo_t) :: thermo_data
    double precision :: temperature, kin_e
    double precision :: v_com(3)
    double precision :: com_pos(3)
    double precision :: unit_r(3)
    type(particle_system_io_t) :: dimer_io
    type(particle_system_io_t) :: solvent_io
    double precision :: bulk_rate
  