I have a fortran code in which I have a parallel part. It is compiled by `gfortran` successfully, but I get a segmentation fault by running it. The serial compiled run file does not show any fault. Also I have examined the parallel program with very small input matrix (rho1 & rho2) and tested the step by step parameters. There were no fault. If I understand correctly, when I determine the variables as `PRIVATE`, there is no need to use 
`$OMP ATOMIC`. Here the matrices rho1 and rho2, have a dimension of about 15,000,000. Here is the parallel part of code:

```
!$OMP PARALLEL DO ORDERED DEFAULT(PRIVATE)
  do ix = 1 , nx
    do iy = 1 , ny
      do iz = 1 , nz
         k = iz + (iy-1) * nz + (ix-1) * ny * nz
         if (rho1(k) .GT. 0.d0) then
           x1 = x0 + ((ix-1) * dx)
           y1 = y0 + ((iy-1) * dy)
           z1 = z0 + ((iz-1) * dz)
           rr = (x1-xa)**2 + (y1-ya)**2 + (z1-za)**2
           r1a = dsqrt (rr)
           rr = (x1-xb)**2 + (y1-yb)**2 + (z1-zb)**2
           r1b = dsqrt (rr)
           if (r1a == 0.d0) Vnuc = (rho1(k) * Znb)/r1b
           if (r1b == 0.d0) Vnuc = (rho1(K) * Zna)/r1a
           if (r1a .GT. 0.d0 .AND. r1b .GT. 0.d0) then
             Vnuc = (rho1(k) * Zna)/r1a + (rho1(K) * Znb)/r1b
           endif
           Ve = 0
           !$OMP ORDERED
           j = 1
           do jx = 1 , nx
            do jy = 1 , ny
             do jz = 1 , nz
               if (rho2(j) .GT. 0.d0) then
                x2 = x0 + ((jx-1) * dx)
                y2 = y0 + ((jy-1) * dy)
                z2 = z0 + ((jz-1) * dz)
                rr= (x1-x2)**2 + (y1-y2)**2 + (z1-z2)**2
                r12 = dsqrt (rr)
                if (r12 .GT. 0.d0) then
                 Ve = Ve + (rho1(k)*rho2(j))/r12
                endif
               endif
               j = j + 1
             enddo
            enddo
           enddo
           !$OMP END ORDERED
           V1 = (Ve * dx * dy * dz * 0.529177d0) - Vnuc
           rr = (x1-xmid)**2 + (y1-ymid)**2 + (z1-zmid)**2
           r = dsqrt (rr)
           zef1(k) = V1 * r            
          endif
       enddo
    enddo
  enddo
  !$OMP END PARALLEL DO

```