diff --git a/src/Davidson/u0Hu0.irp.f b/src/Davidson/u0Hu0.irp.f
index 18004e02..e34ba3ce 100644
--- a/src/Davidson/u0Hu0.irp.f
+++ b/src/Davidson/u0Hu0.irp.f
@@ -344,50 +344,7 @@ subroutine H_S2_u_0_nstates(v_0,s_0,u_0,H_jj,S2_jj,n,keys_tmp,Nint,N_st,sze_8)
   Vt = 0.d0
   St = 0.d0
 
-  !$OMP DO SCHEDULE(guided)
-  do sh=1,shortcut(0,1)
-    do sh2=sh,shortcut(0,1)
-      exa = 0
-      do ni=1,Nint
-        exa = exa + popcnt(xor(version(ni,sh,1), version(ni,sh2,1)))
-      end do
-      if(exa > 2) then
-        cycle
-      end if
-
-      do i=shortcut(sh,1),shortcut(sh+1,1)-1
-        org_i = sort_idx(i,1)
-        if(sh==sh2) then
-          endi = i-1
-        else
-          endi = shortcut(sh2+1,1)-1
-        end if
-        do ni=1,Nint
-          sorted_i(ni) = sorted(ni,i,1)
-        enddo
-
-        do j=shortcut(sh2,1),endi
-          org_j = sort_idx(j,1)
-          ext = exa
-          do ni=1,Nint
-            ext = ext + popcnt(xor(sorted_i(ni), sorted(ni,j,1)))
-          end do
-          if(ext <= 4) then
-            call i_h_j (keys_tmp(1,1,org_j),keys_tmp(1,1,org_i),nint,hij)
-            call get_s2(keys_tmp(1,1,org_j),keys_tmp(1,1,org_i),nint,s2)
-            do istate=1,n_st
-              vt (istate,org_i) = vt (istate,org_i) + hij*ut(istate,org_j)
-              vt (istate,org_j) = vt (istate,org_j) + hij*ut(istate,org_i)
-              st (istate,org_i) = st (istate,org_i) + s2*ut(istate,org_j)
-              st (istate,org_j) = st (istate,org_j) + s2*ut(istate,org_i)
-            enddo
-          endif
-        enddo
-      enddo
-    enddo
-  enddo
-  !$OMP END DO 
-  !$OMP DO SCHEDULE(guided)
+  !$OMP DO SCHEDULE(static,1)
   do sh=1,shortcut(0,2)
     do i=shortcut(sh,2),shortcut(sh+1,2)-1
       org_i = sort_idx(i,2)
@@ -410,16 +367,67 @@ subroutine H_S2_u_0_nstates(v_0,s_0,u_0,H_jj,S2_jj,n,keys_tmp,Nint,N_st,sze_8)
       end do
     end do
   enddo
-  !$OMP END DO 
+  !$OMP END DO NOWAIT
+  do sh=1,shortcut(0,1)
+    !$OMP DO SCHEDULE(static,1)
+    do sh2=sh,shortcut(0,1)
+      exa = 0
+      do ni=1,Nint
+        exa = exa + popcnt(xor(version(ni,sh,1), version(ni,sh2,1)))
+      end do
+      if(exa > 2) then
+        cycle
+      end if
 
-  !$OMP CRITICAL
+      do i=shortcut(sh,1),shortcut(sh+1,1)-1
+        org_i = sort_idx(i,1)
+        if(sh==sh2) then
+          endi = i-1
+        else
+          endi = shortcut(sh2+1,1)-1
+        end if
+        do ni=1,Nint
+          sorted_i(ni) = sorted(ni,i,1)
+        enddo
+
+        do j=shortcut(sh2,1),endi
+          ext = exa
+          do ni=1,Nint
+            ext = ext + popcnt(xor(sorted_i(ni), sorted(ni,j,1)))
+          end do
+          if(ext <= 4) then
+            org_j = sort_idx(j,1)
+            call i_h_j (keys_tmp(1,1,org_j),keys_tmp(1,1,org_i),nint,hij)
+            if (hij /= 0.d0) then
+              do istate=1,n_st
+                vt (istate,org_i) = vt (istate,org_i) + hij*ut(istate,org_j)
+                vt (istate,org_j) = vt (istate,org_j) + hij*ut(istate,org_i)
+              enddo
+            endif
+            if (ext /= 2) then
+              call get_s2(keys_tmp(1,1,org_j),keys_tmp(1,1,org_i),nint,s2)
+              if (s2 /= 0.d0) then
+                do istate=1,n_st
+                  st (istate,org_i) = st (istate,org_i) + s2*ut(istate,org_j)
+                  st (istate,org_j) = st (istate,org_j) + s2*ut(istate,org_i)
+                enddo
+              endif
+            endif
+          endif
+        enddo
+      enddo
+    enddo
+    !$OMP END DO NOWAIT
+  enddo
+
+  !$OMP CRITICAL (u0Hu0)
   do istate=1,N_st
     do i=n,1,-1
       v_0(i,istate) = v_0(i,istate) + vt(istate,i)
       s_0(i,istate) = s_0(i,istate) + st(istate,i)
     enddo
   enddo
-  !$OMP END CRITICAL
+  !$OMP END CRITICAL (u0Hu0)
 
   deallocate(vt,st)
   !$OMP END PARALLEL