anchor.diff:    dimer_io%id_info%store = .false.
     dimer_io%position_info%store = .true.
     dimer_io%position_info%mode = ior(H5MD_LINEAR,H5MD_STORE_TIME)
  -  dimer_io%position_info%step = N_loop
  -  dimer_io%position_info%time = N_loop*dt
  +  dimer_io%position_info%step = N_MD_steps
  +  dimer_io%position_info%time = N_MD_steps*dt
     dimer_io%image_info%store = .true.
     dimer_io%image_info%mode = ior(H5MD_LINEAR,H5MD_STORE_TIME)
  -  dimer_io%image_info%step = N_loop
  -  dimer_io%image_info%time = N_loop*dt
  +  dimer_io%image_info%step = N_MD_steps
  +  dimer_io%image_info%time = N_MD_steps*dt
     dimer_io%velocity_info%store = .true.
     dimer_io%velocity_info%mode = ior(H5MD_LINEAR,H5MD_STORE_TIME)
  -  dimer_io%velocity_info%step = N_loop
  -  dimer_io%velocity_info%time = N_loop*dt
  +  dimer_io%velocity_info%step = N_MD_steps
  +  dimer_io%velocity_info%time = N_MD_steps*dt
     dimer_io%species_info%store = .true.
  -  dimer_io%species_info%mode = ior(H5MD_LINEAR,H5MD_STORE_TIME)
  +  dimer_io%species_info%mode = H5MD_FIXED
     call dimer_io%init(hfile, 'dimer', colloids)
  +
  +  solvent_io%force_info%store = .false.
  +  solvent_io%id_info%store = .false.
  +  solvent_io%position_info%store = .true.
  +  solvent_io%position_info%mode = ior(H5MD_LINEAR,H5MD_STORE_TIME)
  +  solvent_io%position_info%step = N_loop*N_MD_steps
  +  solvent_io%position_info%time = N_loop*N_MD_steps*dt
  +  solvent_io%image_info%store = .true.
  +  solvent_io%image_info%mode = ior(H5MD_LINEAR,H5MD_STORE_TIME)
  +  solvent_io%image_info%step = N_loop*N_MD_steps
  +  solvent_io%image_info%time = N_loop*N_MD_steps*dt
  +  solvent_io%velocity_info%store = .true.
  +  solvent_io%velocity_info%mode = ior(H5MD_LINEAR,H5MD_STORE_TIME)
  +  solvent_io%velocity_info%step = N_loop*N_MD_steps
  +  solvent_io%velocity_info%time = N_loop*N_MD_steps*dt
  +  solvent_io%species_info%store = .true.
  +  solvent_io%species_info%mode = ior(H5MD_LINEAR,H5MD_STORE_TIME)
  +  solvent_io%species_info%step = N_loop*N_MD_steps
  +  solvent_io%species_info%time = N_loop*N_MD_steps*dt
  +  call solvent_io%init(hfile, 'solvent', solvent)
   
     call random_number(solvent% vel(:, :))
     solvent% vel = (solvent% vel - 0.5d0)*sqrt(12*T)
  
positive.code:   colloids% pos(1,2) = colloids% pos(1,2) + d
  
    call h5gcreate_f(dimer_io%group, 'box', box_group, error)
    call h5md_write_attribute(box_group, 'dimension', 3)
    call dummy_element%create_fixed(box_group, 'edges', solvent_cells%edges)
    call h5gclose_f(box_group, error)
  
negative.code: 
    write(*,*) 'n extra sorting', n_extra_sorting
  
    call solvent_io%position%append(solvent%pos)
    call solvent_io%velocity%append(solvent%vel)
    call solvent_io%image%append(solvent%image)
    call solvent_io%species%append(solvent%species)
  
    call dimer_io%close()
    call solvent_io%close()
    call hfile%close()
    call h5close_f(error)
  
  