anchor.diff:    integer :: n_threads
     type(h5md_file_t) :: hfile
     type(h5md_element_t) :: dummy_element
  -  integer(HID_T) :: fields_group
  +  integer(HID_T) :: fields_group, params_group
     integer(HID_T) :: connectivity_group
     integer(HID_T) :: box_group
     integer(HID_T) :: tmp_id
  
positive.code:   solvent% force_old = solvent% force
    colloids% force_old = colloids% force
  
    write(*,*) 'Running for', N_loop, 'loops'
    call main%tic()
    do i = 1, N_loop
       if (modulo(i,5) == 0) write(*,'(i05)',advance='no') i
       md_loop: do j = 1, N_MD_steps
          call md_pos(solvent, dt)
  
  
negative.code:   write(*,*) ''
  
    write(*,*) 'n extra sorting', n_extra_sorting
  
    ! create a group for block correlators and write the data
  
    call h5gcreate_f(hfile%id, 'block_correlators', correlator_group, error)
    call axial_cf%write(correlator_group, N_MD_steps, N_MD_steps*dt, 1, dt)
    call h5gclose_f(correlator_group, error)
  
    ! write solvent coordinates for last step
  
    call thermo_data%append(hfile, temperature, e1+e2, kin_e, e1+e2+kin_e, v_com, add=.false., force=.true.)
    call solvent_io%position%append(solvent%pos)
  