anchor.diff:      end do
   
       call n_list%time_force%tic()
  -    !$omp parallel do private(x, s1, f1, j, idx, s2, d, r_sq, f) &
  +    !$omp parallel do private(x, s1, f1, j, idx, s2, d, r_sq, f, MASK) &
       !$omp& reduction(+:e)
       do i = 1, ps1% Nmax
          if (ps1% species(i) <= 0) continue
  
positive.code:              ps2%force(2, idx) = ps2% force(2,idx) - f(2)
               !$omp atomic
               ps2%force(3, idx) = ps2% force(3,idx) - f(3)
               !$omp atomic
               ps2%flags(idx) = ior(ps2%flags(idx), MD_MASK)
            end if
         end do
         ps1% force(:, i) = ps1% force(:, i) + f1
  
negative.code: 
      integer :: i, j
      integer :: idx
      integer :: MASK
      integer :: n_species1, n_species2
      double precision :: x(3), d(3), f(3), f1(3)
      integer :: s1, s2
  