anchor.diff:  
     call solvent_colloid_lj% init(epsilon, sigma, sigma_cut)
   
  -  epsilon(1,1) = PTread_d(config, 'epsilon_C_C')
  -  epsilon(1,2) = PTread_d(config, 'epsilon_N_C')
  -  epsilon(2,1) = PTread_d(config, 'epsilon_N_C')
  -  epsilon(2,2) = PTread_d(config, 'epsilon_N_N')
  +  epsilon(1,1) = PTread_d(config, 'epsilon_C_C', loc=params_group)
  +  epsilon(1,2) = PTread_d(config, 'epsilon_N_C', loc=params_group)
  +  epsilon(2,1) = epsilon(1,2)
  +  epsilon(2,2) = PTread_d(config, 'epsilon_N_N', loc=params_group)
   
     sigma(1,1) = 2*sigma_C
     sigma(1,2) = sigma_C + sigma_N
  
positive.code: 
    call colloids% init(2,2, mass) !there will be 2 species of colloids
  
    call hfile%create(args%output_file, 'RMPCDMD::single_dimer_pbc', &
         'N/A', 'Pierre de Buyl')
    call thermo_data%init(hfile, n_buffer=50, step=N_MD_steps, time=N_MD_steps*dt)
  
    call PTkill(config)
    
    colloids% species(1) = 1
  
negative.code:   integer :: n_threads
    type(h5md_file_t) :: hfile
    type(h5md_element_t) :: dummy_element
    integer(HID_T) :: fields_group, params_group
    integer(HID_T) :: box_group
    type(thermo_t) :: thermo_data
    double precision :: temperature, kin_e
  