anchor.diff:  
     call neigh% make_stencil(solvent_cells, max_cut+skin)
   
  -  call neigh% update_list(colloids, solvent, max_cut+skin, solvent_cells)
  +  call neigh% update_list(colloids, solvent, max_cut+skin, solvent_cells, solvent_colloid_lj)
   
     cyl_shell_rmin = max(sigma_N, sigma_C)
     cyl_shell_rmax = cyl_shell_rmin + 2
  
positive.code:      call solvent_cells%random_shift(state(1))
       call varia%tac()
  
       call solvent% sort(solvent_cells)
       call neigh% update_list(colloids, solvent, max_cut+skin, solvent_cells)
       call varia%tic()
       !$omp parallel do
       do k = 1, solvent%Nmax
  
negative.code:            call apply_pbc(colloids, solvent_cells% edges)
             call varia%tac()
             call solvent% sort(solvent_cells)
             call neigh% update_list(colloids, solvent, max_cut + skin, solvent_cells, solvent_colloid_lj)
             call varia%tic()
             !$omp parallel do
             do k = 1, solvent%Nmax
  