anchor.diff:    call colloid_lj% init( reshape( [ epsilon ], [1, 1] ), &
          reshape( [ sigma ], [1, 1] ), reshape( [ sigma_cut ], [1, 1] ) )
   
  -  mass = 3000.d0 / (L(1)*L(2)*L(3)) * sigma**3 * 4 * 3.141/3
  +  mass = rho * sigma**3 * 4 * 3.141/3
  +  write(*,*) 'mass =', mass
   
     call solvent% init(N)
   
  -  call colloids% init_from_file('input_data.h5', 'colloids', H5MD_LINEAR, 4)
  +  call colloids% init(1)
  +  
  +  open(15,file ='data14.txt')
  +  
     write(*, *) colloids% pos
     colloids% species = 1
     colloids% vel = 0
  -
  +  
     call random_number(solvent% vel(:, :))
     solvent% vel = (solvent% vel - 0.5d0)*sqrt(6.d0*2)
     solvent% vel = solvent% vel - spread(sum(solvent% vel, dim=2)/solvent% Nmax, 2, solvent% Nmax)
  
positive.code:   solvent% species = 1
  
    call solvent_cells%init(L, 1.d0)
  
    call solvent% random_placement(solvent_cells% edges, colloids, solvent_colloid_lj)
  
    call solvent% sort(solvent_cells)
  
negative.code:   type(lj_params_t) :: solvent_colloid_lj
    type(lj_params_t) :: colloid_lj
  
    integer, parameter :: rho = 10
    integer :: N
    integer :: error
  
    double precision :: epsilon, sigma, sigma_cut
  