anchor.diff:    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)
  +
  +  call h5gcreate_f(solvent_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)
  
positive.code: 
    write(*,*) 'n extra sorting', n_extra_sorting
  
    call dimer_io%close()
    call hfile%close()
    call h5close_f(error)
  
  
negative.code:   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_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_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_MD_steps
    dimer_io%velocity_info%time = N_MD_steps*dt
    dimer_io%species_info%store = .true.
    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)
  