diff --git a/src/Davidson/diagonalization_hs2.irp.f b/src/Davidson/diagonalization_hs2.irp.f
index 8a4cb2d2..778a5702 100644
--- a/src/Davidson/diagonalization_hs2.irp.f
+++ b/src/Davidson/diagonalization_hs2.irp.f
@@ -223,6 +223,7 @@ subroutine davidson_diag_hjj_sjj(dets_in,u_in,H_jj,S2_jj,energies,dim_in,sze,N_s
       ! -----------------------------------------
       
        
+!      call H_S2_u_0_nstates_zmq(W(1,shift+1),S(1,shift+1),U(1,shift+1),H_jj,S2_jj,sze,dets_in,Nint,N_st_diag,sze_8)
       call H_S2_u_0_nstates(W(1,shift+1),S(1,shift+1),U(1,shift+1),H_jj,S2_jj,sze,dets_in,Nint,N_st_diag,sze_8)
       
       
diff --git a/src/Davidson/u0Hu0.irp.f b/src/Davidson/u0Hu0.irp.f
index 9ab30476..d13b4db4 100644
--- a/src/Davidson/u0Hu0.irp.f
+++ b/src/Davidson/u0Hu0.irp.f
@@ -177,7 +177,7 @@ BEGIN_PROVIDER [ double precision, psi_energy, (N_states) ]
 END_PROVIDER
 
 
-subroutine H_S2_u_0_nstates(v_0,s_0,u_0,H_jj,S2_jj,n,keys_tmp,Nint,N_st,sze_8)
+subroutine H_S2_u_0_nstates_zmq(v_0,s_0,u_0,H_jj,S2_jj,n,keys_tmp,Nint,N_st,sze_8)
   use bitmasks
   use f77_zmq
   implicit none
@@ -280,3 +280,156 @@ end
 
 
 
+subroutine H_S2_u_0_nstates(v_0,s_0,u_0,H_jj,S2_jj,n,keys_tmp,Nint,N_st,sze_8)
+  use bitmasks
+  implicit none
+  BEGIN_DOC
+  ! Computes v_0 = H|u_0> and s_0 = S^2 |u_0>
+  !
+  ! n : number of determinants
+  !
+  ! H_jj : array of <j|H|j>
+  !
+  ! S2_jj : array of <j|S^2|j>
+  END_DOC
+  integer, intent(in)            :: N_st,n,Nint, sze_8
+  double precision, intent(out)  :: v_0(sze_8,N_st), s_0(sze_8,N_st)
+  double precision, intent(in)   :: u_0(sze_8,N_st)
+  double precision, intent(in)   :: H_jj(n), S2_jj(n)
+  integer(bit_kind),intent(in)   :: keys_tmp(Nint,2,n)
+  double precision               :: hij,s2 
+  double precision, allocatable  :: vt(:,:), ut(:,:), st(:,:)
+  integer                        :: i,j,k,l, jj,ii
+  integer                        :: i0, j0
+  
+  integer, allocatable           :: shortcut(:,:), sort_idx(:,:)
+  integer(bit_kind), allocatable :: sorted(:,:,:), version(:,:,:)
+  integer(bit_kind)              :: sorted_i(Nint)
+  
+  integer                        :: sh, sh2, ni, exa, ext, org_i, org_j, endi, istate
+  integer                        :: N_st_8
+  
+  integer, external              :: align_double
+  integer :: blockb, blockb2, istep
+  double precision :: ave_workload, workload, target_workload_inv
+  
+  !DIR$ ATTRIBUTES ALIGN : $IRP_ALIGN :: vt, ut
+
+  N_st_8 = align_double(N_st)
+
+  ASSERT (Nint > 0)
+  ASSERT (Nint == N_int)
+  ASSERT (n>0)
+  PROVIDE ref_bitmask_energy
+
+  allocate (shortcut(0:n+1,2), sort_idx(n,2), sorted(Nint,n,2), version(Nint,n,2))
+  allocate(ut(N_st_8,n))
+
+  v_0 = 0.d0
+  s_0 = 0.d0
+
+  do i=1,n
+    do istate=1,N_st
+      ut(istate,i) = u_0(i,istate)
+    enddo
+  enddo
+
+  call sort_dets_ab_v(keys_tmp, sorted(1,1,1), sort_idx(1,1), shortcut(0,1), version(1,1,1), n, Nint)
+  call sort_dets_ba_v(keys_tmp, sorted(1,1,2), sort_idx(1,2), shortcut(0,2), version(1,1,2), n, Nint)
+
+  !$OMP PARALLEL DEFAULT(NONE)                                       &
+      !$OMP PRIVATE(i,hij,s2,j,k,jj,vt,st,ii,sh,sh2,ni,exa,ext,org_i,org_j,endi,sorted_i,istate)&
+      !$OMP SHARED(n,keys_tmp,ut,Nint,v_0,s_0,sorted,shortcut,sort_idx,version,N_st,N_st_8) 
+  allocate(vt(N_st_8,n),st(N_st_8,n))
+  Vt = 0.d0
+  St = 0.d0
+
+  !$OMP DO SCHEDULE(dynamic)
+  do sh=1,shortcut(0,1)
+    do sh2=sh,shortcut(0,1)
+      exa = 0
+      do ni=1,Nint
+        exa = exa + popcnt(xor(version(ni,sh,1), version(ni,sh2,1)))
+      end do
+      if(exa > 2) then
+        cycle
+      end if
+
+      do i=shortcut(sh,1),shortcut(sh+1,1)-1
+        org_i = sort_idx(i,1)
+        if(sh==sh2) then
+          endi = i-1
+        else
+          endi = shortcut(sh2+1,1)-1
+        end if
+        do ni=1,Nint
+          sorted_i(ni) = sorted(ni,i,1)
+        enddo
+
+        do j=shortcut(sh2,1),endi
+          org_j = sort_idx(j,1)
+          ext = exa
+          do ni=1,Nint
+            ext = ext + popcnt(xor(sorted_i(ni), sorted(ni,j,1)))
+          end do
+          if(ext <= 4) then
+            call i_h_j (keys_tmp(1,1,org_j),keys_tmp(1,1,org_i),nint,hij)
+            call get_s2(keys_tmp(1,1,org_j),keys_tmp(1,1,org_i),nint,s2)
+            do istate=1,n_st
+              vt (istate,org_i) = vt (istate,org_i) + hij*ut(istate,org_j)
+              vt (istate,org_j) = vt (istate,org_j) + hij*ut(istate,org_i)
+              st (istate,org_i) = st (istate,org_i) + s2*ut(istate,org_j)
+              st (istate,org_j) = st (istate,org_j) + s2*ut(istate,org_i)
+            enddo
+          endif
+        enddo
+      enddo
+    enddo
+  enddo
+  !$OMP END DO NOWAIT
+  !$OMP DO SCHEDULE(dynamic)
+  do sh=1,shortcut(0,2)
+    do i=shortcut(sh,2),shortcut(sh+1,2)-1
+      org_i = sort_idx(i,2)
+      do j=shortcut(sh,2),i-1
+        org_j = sort_idx(j,2)
+        ext = 0
+        do ni=1,Nint
+          ext = ext + popcnt(xor(sorted(ni,i,2), sorted(ni,j,2)))
+        end do
+        if(ext == 4) then
+            call i_h_j (keys_tmp(1,1,org_j),keys_tmp(1,1,org_i),nint,hij)
+            call get_s2(keys_tmp(1,1,org_j),keys_tmp(1,1,org_i),nint,s2)
+            do istate=1,n_st
+              vt (istate,org_i) = vt (istate,org_i) + hij*ut(istate,org_j)
+              vt (istate,org_j) = vt (istate,org_j) + hij*ut(istate,org_i)
+              st (istate,org_i) = st (istate,org_i) + s2*ut(istate,org_j)
+              st (istate,org_j) = st (istate,org_j) + s2*ut(istate,org_i)
+            enddo
+        end if
+      end do
+    end do
+  enddo
+  !$OMP END DO NOWAIT
+
+  !$OMP CRITICAL
+  do istate=1,N_st
+    do i=n,1,-1
+      v_0(i,istate) = v_0(i,istate) + vt(istate,i)
+      s_0(i,istate) = s_0(i,istate) + st(istate,i)
+    enddo
+  enddo
+  !$OMP END CRITICAL
+
+  deallocate(vt,st)
+  !$OMP END PARALLEL
+
+  do istate=1,N_st
+    do i=1,n
+      v_0(i,istate) = v_0(i,istate) + H_jj(i) * u_0(i,istate)
+      s_0(i,istate) = s_0(i,istate) + s2_jj(i)* u_0(i,istate)
+    enddo
+  enddo
+  deallocate (shortcut, sort_idx, sorted, version, ut)
+end
+