diff --git a/src/cipsi/energy.irp.f b/src/cipsi/energy.irp.f
index b7ba42bb..0ae5ad79 100644
--- a/src/cipsi/energy.irp.f
+++ b/src/cipsi/energy.irp.f
@@ -11,9 +11,15 @@ BEGIN_PROVIDER [ double precision, pt2_E0_denominator, (N_states) ]
  BEGIN_DOC
  ! E0 in the denominator of the PT2
  END_DOC
+ integer :: i,j
  if (initialize_pt2_E0_denominator) then
    if (h0_type == "EN") then
      pt2_E0_denominator(1:N_states) = psi_energy(1:N_states)
+   else if (h0_type == "HF") then
+     do i=1,N_states
+       j = maxloc(abs(psi_coef(:,i)),1)
+       pt2_E0_denominator(i) = psi_det_hii(j)
+     enddo
    else if (h0_type == "Barycentric") then
      pt2_E0_denominator(1:N_states) = barycentric_electronic_energy(1:N_states)
    else if (h0_type == "Variance") then
@@ -24,7 +30,9 @@ BEGIN_PROVIDER [ double precision, pt2_E0_denominator, (N_states) ]
      print *,  h0_type, ' not implemented'
      stop
    endif
-  call write_double(6,pt2_E0_denominator(1)+nuclear_repulsion, 'PT2 Energy denominator')
+  do i=1,N_states
+    call write_double(6,pt2_E0_denominator(i)+nuclear_repulsion, 'PT2 Energy denominator')
+  enddo
  else
    pt2_E0_denominator = -huge(1.d0)
  endif
diff --git a/src/cipsi/pt2_stoch_routines.irp.f b/src/cipsi/pt2_stoch_routines.irp.f
index d93d977a..83924bb6 100644
--- a/src/cipsi/pt2_stoch_routines.irp.f
+++ b/src/cipsi/pt2_stoch_routines.irp.f
@@ -248,8 +248,8 @@ subroutine ZMQ_pt2(E, pt2,relative_error, error, variance, norm, N_in)
               + 64.d0*pt2_n_tasks_max           & ! task
               + 3.d0*pt2_n_tasks_max*N_states   & ! pt2, variance, norm
               + 1.d0*pt2_n_tasks_max            & ! i_generator, subset
-              + 2.d0*(N_int*2.d0*N_in + N_in)   & ! selection buffers
-              + 1.d0*(N_int*2.d0*N_in + N_in)   & ! sort/merge selection buffers
+              + 1.d0*(N_int*2.d0*ii+ ii)        & ! selection buffer
+              + 1.d0*(N_int*2.d0*ii+ ii)        & ! sort selection buffer
               + 2.0d0*(ii)                      & ! preinteresting, interesting,
                                                   ! prefullinteresting, fullinteresting
               + 2.0d0*(N_int*2*ii)              & ! minilist, fullminilist
@@ -350,7 +350,8 @@ subroutine pt2_collector(zmq_socket_pull, E, relative_error, pt2, error, varianc
   double precision, allocatable      :: nI(:,:), nI_task(:,:), T3(:)
   integer(ZMQ_PTR),external      :: new_zmq_to_qp_run_socket
   integer(ZMQ_PTR)               :: zmq_to_qp_run_socket
-  integer, external :: zmq_delete_tasks
+  integer, external :: zmq_delete_tasks_async_send
+  integer, external :: zmq_delete_tasks_async_recv
   integer, external :: zmq_abort
   integer, external :: pt2_find_sample_lr
 
@@ -364,7 +365,7 @@ subroutine pt2_collector(zmq_socket_pull, E, relative_error, pt2, error, varianc
 
   integer, allocatable :: f(:)
   logical, allocatable :: d(:)
-  logical :: do_exit, stop_now
+  logical :: do_exit, stop_now, sending
   logical, external :: qp_stop
   type(selection_buffer) :: b2
 
@@ -372,6 +373,8 @@ subroutine pt2_collector(zmq_socket_pull, E, relative_error, pt2, error, varianc
   double precision :: rss
   double precision, external :: memory_of_double, memory_of_int
 
+  sending =.False.
+
   rss  = memory_of_int(pt2_n_tasks_max*2+N_det_generators*2)
   rss += memory_of_double(N_states*N_det_generators)*3.d0
   rss += memory_of_double(N_states*pt2_n_tasks_max)*3.d0
@@ -422,6 +425,7 @@ subroutine pt2_collector(zmq_socket_pull, E, relative_error, pt2, error, varianc
   stop_now = .false.
   do while (n <= N_det_generators)
     if(f(pt2_J(n)) == 0) then
+!print *,  'f(pt2_J(n)) == 0'
       d(pt2_J(n)) = .true.
       do while(d(U+1))
         U += 1
@@ -447,6 +451,7 @@ subroutine pt2_collector(zmq_socket_pull, E, relative_error, pt2, error, varianc
       ! Add Stochastic part
       c = pt2_R(n)
       if(c > 0) then
+!print *,  'c>0'
         x  = 0d0
         x2 = 0d0
         x3 = 0d0
@@ -500,7 +505,7 @@ subroutine pt2_collector(zmq_socket_pull, E, relative_error, pt2, error, varianc
       exit
     else
       call pull_pt2_results(zmq_socket_pull, index, eI_task, vI_task, nI_task, task_id, n_tasks, b2)
-      if (zmq_delete_tasks(zmq_to_qp_run_socket,zmq_socket_pull,task_id,n_tasks,more) == -1) then
+      if (zmq_delete_tasks_async_send(zmq_to_qp_run_socket,task_id,n_tasks,sending) == -1) then
           stop 'Unable to delete tasks'
       endif
       do i=1,n_tasks
@@ -511,12 +516,19 @@ subroutine pt2_collector(zmq_socket_pull, E, relative_error, pt2, error, varianc
       end do
       do i=1, b2%cur
         call add_to_selection_buffer(b, b2%det(1,1,i), b2%val(i))
+        ! We assume the pulled buffer is sorted
         if (b2%val(i) > b%mini) exit
       end do
+      if (zmq_delete_tasks_async_recv(zmq_to_qp_run_socket,more,sending) == -1) then
+          stop 'Unable to delete tasks'
+      endif
     end if
   end do
+!print *,  'deleting b2'
   call delete_selection_buffer(b2)
+!print *,  'sorting b'
   call sort_selection_buffer(b)
+!print *,  'done'
   call end_zmq_to_qp_run_socket(zmq_to_qp_run_socket)
 
 end subroutine
diff --git a/src/cipsi/run_pt2_slave.irp.f b/src/cipsi/run_pt2_slave.irp.f
index 04c28e1b..b4df2def 100644
--- a/src/cipsi/run_pt2_slave.irp.f
+++ b/src/cipsi/run_pt2_slave.irp.f
@@ -1,4 +1,3 @@
-
 subroutine run_pt2_slave(thread,iproc,energy)
   use f77_zmq
   use selection_types
@@ -18,7 +17,7 @@ subroutine run_pt2_slave(thread,iproc,energy)
   integer(ZMQ_PTR), external     :: new_zmq_push_socket
   integer(ZMQ_PTR)               :: zmq_socket_push
 
-  type(selection_buffer) :: b, b2
+  type(selection_buffer) :: b
   logical :: done, buffer_ready
 
   double precision,allocatable :: pt2(:,:), variance(:,:), norm(:,:)
@@ -27,6 +26,9 @@ subroutine run_pt2_slave(thread,iproc,energy)
 
   double precision :: rss
   double precision, external :: memory_of_double, memory_of_int
+  integer :: bsize ! Size of selection buffers
+  logical :: sending
+
   rss  = memory_of_int(pt2_n_tasks_max)*67.d0
   rss += memory_of_double(pt2_n_tasks_max)*(N_states*3)
   call check_mem(rss,irp_here)
@@ -50,6 +52,7 @@ subroutine run_pt2_slave(thread,iproc,energy)
   buffer_ready = .False.
   n_tasks = 1
 
+  sending = .False.
   done = .False.
   n_tasks = 1
   do while (.not.done)
@@ -72,8 +75,8 @@ subroutine run_pt2_slave(thread,iproc,energy)
     enddo
     if (b%N == 0) then
       ! Only first time
-      call create_selection_buffer(N, N*2, b)
-      call create_selection_buffer(N, N*2, b2)
+      bsize = min(N, (elec_alpha_num * (mo_num-elec_alpha_num))**2)
+      call create_selection_buffer(bsize, bsize*2, b)
       buffer_ready = .True.
     else
       ASSERT (N == b%N)
@@ -100,14 +103,14 @@ subroutine run_pt2_slave(thread,iproc,energy)
       done = .true.
     endif
     call sort_selection_buffer(b)
-    call merge_selection_buffers(b,b2)
-    call push_pt2_results(zmq_socket_push, i_generator, pt2, variance, norm, b, task_id, n_tasks)
-    b%mini = b2%mini
+    call push_pt2_results_async_recv(zmq_socket_push,b%mini,sending)
+    call push_pt2_results_async_send(zmq_socket_push, i_generator, pt2, variance, norm, b, task_id, n_tasks,sending)
     b%cur=0
 
-    ! Try to adjust n_tasks around nproc/8 seconds per job
-    n_tasks = min(2*n_tasks,int( dble(n_tasks * nproc/8) / (time1 - time0 + 1.d0)))
+    ! Try to adjust n_tasks around nproc/2 seconds per job
+    n_tasks = min(2*n_tasks,int( dble(n_tasks * nproc/2) / (time1 - time0 + 1.d0)))
   end do
+  call push_pt2_results_async_recv(zmq_socket_push,b%mini,sending)
 
   integer, external :: disconnect_from_taskserver
   do i=1,300
@@ -120,7 +123,6 @@ subroutine run_pt2_slave(thread,iproc,energy)
   call end_zmq_to_qp_run_socket(zmq_to_qp_run_socket)
   if (buffer_ready) then
     call delete_selection_buffer(b)
-    call delete_selection_buffer(b2)
   endif
 end subroutine
 
@@ -226,6 +228,129 @@ IRP_ENDIF
 end subroutine
 
 
+subroutine push_pt2_results_async_send(zmq_socket_push, index, pt2, variance, norm, b, task_id, n_tasks, sending)
+  use f77_zmq
+  use selection_types
+  implicit none
+
+  integer(ZMQ_PTR), intent(in)   :: zmq_socket_push
+  double precision, intent(in)   :: pt2(N_states,n_tasks)
+  double precision, intent(in)   :: variance(N_states,n_tasks)
+  double precision, intent(in)   :: norm(N_states,n_tasks)
+  integer, intent(in) :: n_tasks, index(n_tasks), task_id(n_tasks)
+  type(selection_buffer), intent(inout) :: b
+  logical, intent(inout) :: sending
+  integer :: rc
+
+  if (sending) then
+    print *,  irp_here, ': sending is true'
+    stop -1
+  endif
+  sending = .True.
+
+  rc = f77_zmq_send( zmq_socket_push, n_tasks, 4, ZMQ_SNDMORE)
+  if (rc == -1) then
+    return
+  else if(rc /= 4) then
+    stop 'push'
+  endif
+
+
+  rc = f77_zmq_send( zmq_socket_push, index, 4*n_tasks, ZMQ_SNDMORE)
+  if (rc == -1) then
+    return
+  else if(rc /= 4*n_tasks) then
+    stop 'push'
+  endif
+
+
+  rc = f77_zmq_send( zmq_socket_push, pt2, 8*N_states*n_tasks, ZMQ_SNDMORE)
+  if (rc == -1) then
+    return
+  else if(rc /= 8*N_states*n_tasks) then
+    stop 'push'
+  endif
+
+
+  rc = f77_zmq_send( zmq_socket_push, variance, 8*N_states*n_tasks, ZMQ_SNDMORE)
+  if (rc == -1) then
+    return
+  else if(rc /= 8*N_states*n_tasks) then
+    stop 'push'
+  endif
+
+
+  rc = f77_zmq_send( zmq_socket_push, norm, 8*N_states*n_tasks, ZMQ_SNDMORE)
+  if (rc == -1) then
+    return
+  else if(rc /= 8*N_states*n_tasks) then
+    stop 'push'
+  endif
+
+
+  rc = f77_zmq_send( zmq_socket_push, task_id, n_tasks*4, ZMQ_SNDMORE)
+  if (rc == -1) then
+    return
+  else if(rc /= 4*n_tasks) then
+    stop 'push'
+  endif
+
+
+  rc = f77_zmq_send( zmq_socket_push, b%cur, 4, ZMQ_SNDMORE)
+  if (rc == -1) then
+    return
+  else if(rc /= 4) then
+    stop 'push'
+  endif
+
+
+  rc = f77_zmq_send( zmq_socket_push, b%val, 8*b%cur, ZMQ_SNDMORE)
+  if (rc == -1) then
+    return
+  else if(rc /= 8*b%cur) then
+    stop 'push'
+  endif
+
+
+  rc = f77_zmq_send( zmq_socket_push, b%det, bit_kind*N_int*2*b%cur, 0)
+  if (rc == -1) then
+    return
+  else if(rc /= N_int*2*8*b%cur) then
+    stop 'push'
+  endif
+
+end subroutine
+
+subroutine push_pt2_results_async_recv(zmq_socket_push,mini,sending)
+  use f77_zmq
+  use selection_types
+  implicit none
+
+  integer(ZMQ_PTR), intent(in)    :: zmq_socket_push
+  double precision, intent(out) :: mini
+  logical, intent(inout) :: sending
+  integer :: rc
+
+  if (.not.sending) return
+
+! Activate is zmq_socket_push is a REQ
+IRP_IF ZMQ_PUSH
+IRP_ELSE
+  character*(2) :: ok
+  rc = f77_zmq_recv( zmq_socket_push, ok, 2, 0)
+  if (rc == -1) then
+    return
+  else if ((rc /= 2).and.(ok(1:2) /= 'ok')) then
+    print *,  irp_here//': error in receiving ok'
+    stop -1
+  endif
+  rc = f77_zmq_recv( zmq_socket_push, mini, 8, 0)
+IRP_ENDIF
+  sending = .False.
+end subroutine
+
+
+
 subroutine pull_pt2_results(zmq_socket_pull, index, pt2, variance, norm, task_id, n_tasks, b)
   use f77_zmq
   use selection_types
@@ -315,7 +440,7 @@ subroutine pull_pt2_results(zmq_socket_pull, index, pt2, variance, norm, task_id
 ! Activate is zmq_socket_pull is a REP
 IRP_IF ZMQ_PUSH
 IRP_ELSE
-  rc = f77_zmq_send( zmq_socket_pull, 'ok', 2, 0)
+  rc = f77_zmq_send( zmq_socket_pull, 'ok', 2, ZMQ_SNDMORE)
   if (rc == -1) then
     n_tasks = 1
     task_id(1) = 0
@@ -323,6 +448,7 @@ IRP_ELSE
     print *,  irp_here//': error in sending ok'
     stop -1
   endif
+  rc = f77_zmq_send( zmq_socket_pull, b%mini, 8, 0)
 IRP_ENDIF
 
 end subroutine
diff --git a/src/cipsi/run_selection_slave.irp.f b/src/cipsi/run_selection_slave.irp.f
index 04bb99ef..480ef12b 100644
--- a/src/cipsi/run_selection_slave.irp.f
+++ b/src/cipsi/run_selection_slave.irp.f
@@ -55,12 +55,13 @@ subroutine run_selection_slave(thread,iproc,energy)
     if (done) then
       ctask = ctask - 1
     else
-      integer :: i_generator, N, subset
+      integer :: i_generator, N, subset, bsize
       read(task,*) subset, i_generator, N
       if(buf%N == 0) then
         ! Only first time
-        call create_selection_buffer(N, N*2, buf)
-        call create_selection_buffer(N, N*2, buf2)
+        bsize = min(N, (elec_alpha_num * (mo_num-elec_alpha_num))**2)
+        call create_selection_buffer(bsize, bsize*2, buf)
+!        call create_selection_buffer(N, N*2, buf2)
         buffer_ready = .True.
       else
         ASSERT (N == buf%N)
@@ -83,9 +84,9 @@ subroutine run_selection_slave(thread,iproc,energy)
       end do
       if(ctask > 0) then
         call sort_selection_buffer(buf)
-        call merge_selection_buffers(buf,buf2)
+!        call merge_selection_buffers(buf,buf2)
         call push_selection_results(zmq_socket_push, pt2, variance, norm, buf, task_id(1), ctask)
-        buf%mini = buf2%mini
+!        buf%mini = buf2%mini
         pt2(:) = 0d0
         variance(:) = 0d0
         norm(:) = 0d0
@@ -108,7 +109,7 @@ subroutine run_selection_slave(thread,iproc,energy)
   call end_zmq_push_socket(zmq_socket_push,thread)
   if (buffer_ready) then
     call delete_selection_buffer(buf)
-    call delete_selection_buffer(buf2)
+!    call delete_selection_buffer(buf2)
   endif
 end subroutine
 
diff --git a/src/cipsi/selection.irp.f b/src/cipsi/selection.irp.f
index 86b5536f..69540afc 100644
--- a/src/cipsi/selection.irp.f
+++ b/src/cipsi/selection.irp.f
@@ -153,9 +153,6 @@ subroutine select_singles_and_doubles(i_generator,hole_mask,particle_mask,fock_d
   logical :: monoAdo, monoBdo
   integer :: maskInd
 
-  double precision :: rss
-  double precision, external :: memory_of_double, memory_of_int
-
   PROVIDE psi_bilinear_matrix_columns_loc psi_det_alpha_unique psi_det_beta_unique
   PROVIDE psi_bilinear_matrix_rows psi_det_sorted_order psi_bilinear_matrix_order
   PROVIDE psi_bilinear_matrix_transp_rows_loc psi_bilinear_matrix_transp_columns
@@ -231,7 +228,7 @@ subroutine select_singles_and_doubles(i_generator,hole_mask,particle_mask,fock_d
   
   deallocate(exc_degree)
   nmax=k-1
-  
+
   allocate(iorder(nmax))
   do i=1,nmax
     iorder(i) = i
@@ -241,8 +238,8 @@ subroutine select_singles_and_doubles(i_generator,hole_mask,particle_mask,fock_d
   
   allocate(preinteresting(0:32), prefullinteresting(0:32),     &
       interesting(0:32), fullinteresting(0:32))
-  preinteresting(0) = 0
-  prefullinteresting(0) = 0
+  preinteresting(:) = 0
+  prefullinteresting(:) = 0
   
   do i=1,N_int
     negMask(i,1) = not(psi_det_generators(i,1,i_generator))
@@ -645,13 +642,11 @@ subroutine splash_pq(mask, sp, det, i_gen, N_sel, bannedOrb, banned, mat, intere
     negMask(i,2) = not(mask(i,2))
   end do
 
-  do i=1, N_sel ! interesting(0)
-    !i = interesting(ii)
+  do i=1, N_sel 
     if (interesting(i) < 0) then
       stop 'prefetch interesting(i) and det(i)'
     endif
 
-
     mobMask(1,1) = iand(negMask(1,1), det(1,1,i))
     mobMask(1,2) = iand(negMask(1,2), det(1,2,i))
     nt = popcnt(mobMask(1, 1)) + popcnt(mobMask(1, 2))
@@ -682,10 +677,10 @@ subroutine splash_pq(mask, sp, det, i_gen, N_sel, bannedOrb, banned, mat, intere
         end if
     end if
 
-    call bitstring_to_list_in_selection(mobMask(1,1), p(1,1), p(0,1), N_int)
-    call bitstring_to_list_in_selection(mobMask(1,2), p(1,2), p(0,2), N_int)
-
     if (interesting(i) >= i_gen) then
+        call bitstring_to_list_in_selection(mobMask(1,1), p(1,1), p(0,1), N_int)
+        call bitstring_to_list_in_selection(mobMask(1,2), p(1,2), p(0,2), N_int)
+
         perMask(1,1) = iand(mask(1,1), not(det(1,1,i)))
         perMask(1,2) = iand(mask(1,2), not(det(1,2,i)))
         do j=2,N_int
@@ -704,9 +699,14 @@ subroutine splash_pq(mask, sp, det, i_gen, N_sel, bannedOrb, banned, mat, intere
         else
           call get_d0(det(1,1,i), phasemask, bannedOrb, banned, mat, mask, h, p, sp, psi_selectors_coef_transp(1, interesting(i)))
         end if
-    else
-        if(nt == 4) call past_d2(banned, p, sp)
-        if(nt == 3) call past_d1(bannedOrb, p)
+    else if(nt == 4) then
+        call bitstring_to_list_in_selection(mobMask(1,1), p(1,1), p(0,1), N_int)
+        call bitstring_to_list_in_selection(mobMask(1,2), p(1,2), p(0,2), N_int)
+        call past_d2(banned, p, sp)
+    else if(nt == 3) then
+        call bitstring_to_list_in_selection(mobMask(1,1), p(1,1), p(0,1), N_int)
+        call bitstring_to_list_in_selection(mobMask(1,2), p(1,2), p(0,2), N_int)
+        call past_d1(bannedOrb, p)
     end if
   end do
 
diff --git a/src/cipsi/selection_buffer.irp.f b/src/cipsi/selection_buffer.irp.f
index ce7f2d8b..91fdcd3a 100644
--- a/src/cipsi/selection_buffer.irp.f
+++ b/src/cipsi/selection_buffer.irp.f
@@ -2,6 +2,10 @@
 subroutine create_selection_buffer(N, siz_, res)
   use selection_types
   implicit none
+  BEGIN_DOC
+! Allocates the memory for a selection buffer.
+! The arrays have dimension siz_ and the maximum number of elements is N
+  END_DOC
 
   integer, intent(in) :: N, siz_
   type(selection_buffer), intent(out) :: res
diff --git a/src/cipsi/slave_cipsi.irp.f b/src/cipsi/slave_cipsi.irp.f
index 66560720..0de07e67 100644
--- a/src/cipsi/slave_cipsi.irp.f
+++ b/src/cipsi/slave_cipsi.irp.f
@@ -251,8 +251,8 @@ subroutine run_slave_main
                 + 64.d0*pt2_n_tasks_max           & ! task
                 + 3.d0*pt2_n_tasks_max*N_states   & ! pt2, variance, norm
                 + 1.d0*pt2_n_tasks_max            & ! i_generator, subset
-                + 2.d0*(N_int*2.d0*N_det+ N_det)  & ! selection buffers
-                + 1.d0*(N_int*2.d0*N_det+ N_det)  & ! sort/merge selection buffers
+                + 2.d0*(N_int*2.d0*ii+ ii)        & ! selection buffer
+                + 1.d0*(N_int*2.d0*ii+ ii)        & ! sort selection buffer
                 + 2.0d0*(ii)                      & ! preinteresting, interesting,
                                                     ! prefullinteresting, fullinteresting
                 + 2.0d0*(N_int*2*ii)              & ! minilist, fullminilist
diff --git a/src/cipsi/stochastic_cipsi.irp.f b/src/cipsi/stochastic_cipsi.irp.f
index 9841a429..791656ce 100644
--- a/src/cipsi/stochastic_cipsi.irp.f
+++ b/src/cipsi/stochastic_cipsi.irp.f
@@ -10,7 +10,7 @@ subroutine run_stochastic_cipsi
 
   double precision :: rss
   double precision, external :: memory_of_double
-  PROVIDE H_apply_buffer_allocated
+  PROVIDE H_apply_buffer_allocated N_generators_bitmask
 
   threshold_generators = 1.d0
   SOFT_TOUCH threshold_generators
diff --git a/src/davidson/davidson_parallel.irp.f b/src/davidson/davidson_parallel.irp.f
index b4cb3c7d..c615fae7 100644
--- a/src/davidson/davidson_parallel.irp.f
+++ b/src/davidson/davidson_parallel.irp.f
@@ -139,6 +139,8 @@ subroutine davidson_slave_work(zmq_to_qp_run_socket, zmq_socket_push, N_st, sze,
   ! Run tasks
   ! ---------
 
+  logical :: sending
+  sending=.False.
 
   allocate(v_t(N_st,N_det), s_t(N_st,N_det))
   do
@@ -158,9 +160,11 @@ subroutine davidson_slave_work(zmq_to_qp_run_socket, zmq_socket_push, N_st, sze,
     if (task_done_to_taskserver(zmq_to_qp_run_socket,worker_id,task_id) == -1) then
         print *,  irp_here, 'Unable to send task_done'
     endif
-    call davidson_push_results(zmq_socket_push, v_t, s_t, imin, imax, task_id)
+    call davidson_push_results_async_recv(zmq_socket_push, sending)
+    call davidson_push_results_async_send(zmq_socket_push, v_t, s_t, imin, imax, task_id, sending)
   end do
   deallocate(u_t,v_t, s_t)
+  call davidson_push_results_async_recv(zmq_socket_push, sending)
 
 end subroutine
 
@@ -210,6 +214,73 @@ IRP_ENDIF
 
 end subroutine
 
+subroutine davidson_push_results_async_send(zmq_socket_push, v_t, s_t, imin, imax, task_id,sending)
+  use f77_zmq
+  implicit none
+  BEGIN_DOC
+! Push the results of $H | U \rangle$ from a worker to the master.
+  END_DOC
+
+  integer(ZMQ_PTR)    ,intent(in)    :: zmq_socket_push
+  integer             ,intent(in)    :: task_id, imin, imax
+  double precision    ,intent(in)    :: v_t(N_states_diag,N_det)
+  double precision    ,intent(in)    :: s_t(N_states_diag,N_det)
+  logical             ,intent(inout) :: sending
+  integer                            :: rc, sz
+  integer*8                          :: rc8
+
+  if (sending) then
+    print *,  irp_here, ': sending=true'
+    stop -1
+  endif
+  sending = .True.
+
+  sz = (imax-imin+1)*N_states_diag
+
+  rc = f77_zmq_send( zmq_socket_push, task_id, 4, ZMQ_SNDMORE)
+  if(rc /= 4) stop 'davidson_push_results failed to push task_id'
+
+  rc = f77_zmq_send( zmq_socket_push, imin, 4, ZMQ_SNDMORE)
+  if(rc /= 4) stop 'davidson_push_results failed to push imin'
+
+  rc = f77_zmq_send( zmq_socket_push, imax, 4, ZMQ_SNDMORE)
+  if(rc /= 4) stop 'davidson_push_results failed to push imax'
+
+  rc8 = f77_zmq_send8( zmq_socket_push, v_t(1,imin), 8_8*sz, ZMQ_SNDMORE)
+  if(rc8 /= 8_8*sz) stop 'davidson_push_results failed to push vt'
+
+  rc8 = f77_zmq_send8( zmq_socket_push, s_t(1,imin), 8_8*sz, 0)
+  if(rc8 /= 8_8*sz) stop 'davidson_push_results failed to push st'
+
+end subroutine
+
+subroutine davidson_push_results_async_recv(zmq_socket_push,sending)
+  use f77_zmq
+  implicit none
+  BEGIN_DOC
+! Push the results of $H | U \rangle$ from a worker to the master.
+  END_DOC
+
+  integer(ZMQ_PTR)    ,intent(in)    :: zmq_socket_push
+  logical             ,intent(inout) :: sending
+
+  integer                            :: rc
+
+  if (.not.sending) return
+! Activate is zmq_socket_push is a REQ
+IRP_IF ZMQ_PUSH
+IRP_ELSE
+  character*(2) :: ok
+  rc = f77_zmq_recv( zmq_socket_push, ok, 2, 0)
+  if ((rc /= 2).and.(ok(1:2)/='ok')) then
+    print *, irp_here, ': f77_zmq_recv( zmq_socket_push, ok, 2, 0)'
+    stop -1
+  endif
+IRP_ENDIF
+  sending = .False.
+
+end subroutine
+
 
 
 subroutine davidson_pull_results(zmq_socket_pull, v_t, s_t, imin, imax, task_id)
@@ -275,22 +346,28 @@ subroutine davidson_collector(zmq_to_qp_run_socket, zmq_socket_pull, v0, s0, sze
   integer                          :: more, task_id, imin, imax
 
   double precision, allocatable :: v_t(:,:), s_t(:,:)
+  logical :: sending
   integer :: i,j
+  integer, external :: zmq_delete_task_async_send
+  integer, external :: zmq_delete_task_async_recv
 
   allocate(v_t(N_st,N_det), s_t(N_st,N_det))
   v0 = 0.d0
   s0 = 0.d0
   more = 1
+  sending = .False.
   do while (more == 1)
     call davidson_pull_results(zmq_socket_pull, v_t, s_t, imin, imax, task_id)
+    if (zmq_delete_task_async_send(zmq_to_qp_run_socket,task_id,sending) == -1) then
+      stop 'Unable to delete task'
+    endif
     do j=1,N_st
       do i=imin,imax
         v0(i,j) = v0(i,j) + v_t(j,i)
         s0(i,j) = s0(i,j) + s_t(j,i)
       enddo
     enddo
-    integer, external :: zmq_delete_task
-    if (zmq_delete_task(zmq_to_qp_run_socket,zmq_socket_pull,task_id,more) == -1) then
+    if (zmq_delete_task_async_recv(zmq_to_qp_run_socket,more,sending) == -1) then
       stop 'Unable to delete task'
     endif
   end do
diff --git a/src/perturbation/h0_type.irp.f b/src/perturbation/h0_type.irp.f
index 17a47ce6..7dd58c2c 100644
--- a/src/perturbation/h0_type.irp.f
+++ b/src/perturbation/h0_type.irp.f
@@ -8,5 +8,6 @@ BEGIN_PROVIDER [ character*32,h0_type ]
  else
    h0_type = 'EN'
  endif
+!   h0_type = 'HF'
 END_PROVIDER
 
diff --git a/src/zmq/utils.irp.f b/src/zmq/utils.irp.f
index 939c7b3a..4c838302 100644
--- a/src/zmq/utils.irp.f
+++ b/src/zmq/utils.irp.f
@@ -246,7 +246,7 @@ IRP_ENDIF
 !    stop 'Unable to set ZMQ_RCVBUF on pull socket'
 !  endif
 
-  rc = f77_zmq_setsockopt(new_zmq_pull_socket,ZMQ_RCVHWM,8,4)
+  rc = f77_zmq_setsockopt(new_zmq_pull_socket,ZMQ_RCVHWM,50,4)
   if (rc /= 0) then
     stop 'Unable to set ZMQ_RCVHWM on pull socket'
   endif
@@ -1085,6 +1085,62 @@ integer function zmq_delete_task(zmq_to_qp_run_socket,zmq_socket_pull,task_id,mo
   endif
 end
 
+integer function zmq_delete_task_async_send(zmq_to_qp_run_socket,task_id,sending)
+  use f77_zmq
+  implicit none
+  BEGIN_DOC
+! When a task is done, it has to be removed from the list of tasks on the qp_run
+! queue. This guarantees that the results have been received in the pull.
+  END_DOC
+  integer(ZMQ_PTR), intent(in)   :: zmq_to_qp_run_socket
+  integer, intent(in)            :: task_id
+  logical, intent(inout)         :: sending
+  integer                        :: rc
+  character*(512)                :: message
+
+  if (sending) then
+    print *,  irp_here, ': sending=true'
+    stop -1
+  endif
+  zmq_delete_task_async_send = 0
+
+  write(message,*) 'del_task ', zmq_state, task_id
+  rc = f77_zmq_send(zmq_to_qp_run_socket,trim(message),len(trim(message)),0)
+  if (rc /= len(trim(message))) then
+    zmq_delete_task_async_send = -1
+    return
+  endif
+  sending = .True.
+
+end
+
+integer function zmq_delete_task_async_recv(zmq_to_qp_run_socket,more,sending)
+  use f77_zmq
+  implicit none
+  BEGIN_DOC
+! When a task is done, it has to be removed from the list of tasks on the qp_run
+! queue. This guarantees that the results have been received in the pull.
+  END_DOC
+  integer(ZMQ_PTR), intent(in)   :: zmq_to_qp_run_socket
+  integer, intent(out)           :: more
+  logical, intent(inout)         :: sending
+  integer                        :: rc
+  character*(512)                :: message
+  character*(64) :: reply
+  if (.not.sending) return
+  sending = .False.
+  reply = ''
+  rc = f77_zmq_recv(zmq_to_qp_run_socket,reply,64,0)
+  if (reply(16:19) == 'more') then
+    more = 1
+  else if (reply(16:19) == 'done') then
+    more = 0
+  else
+    zmq_delete_task_async_recv = -1
+    return
+  endif
+end
+
 integer function zmq_delete_tasks(zmq_to_qp_run_socket,zmq_socket_pull,task_id,n_tasks,more)
   use f77_zmq
   implicit none
@@ -1128,7 +1184,7 @@ integer function zmq_delete_tasks(zmq_to_qp_run_socket,zmq_socket_pull,task_id,n
   endif
 end
 
-integer function zmq_delete_tasks_async_send(zmq_to_qp_run_socket,zmq_socket_pull,task_id,n_tasks,more)
+integer function zmq_delete_tasks_async_send(zmq_to_qp_run_socket,task_id,n_tasks,sending)
   use f77_zmq
   implicit none
   BEGIN_DOC
@@ -1136,13 +1192,17 @@ integer function zmq_delete_tasks_async_send(zmq_to_qp_run_socket,zmq_socket_pul
 ! queue. This guarantees that the results have been received in the pull.
   END_DOC
   integer(ZMQ_PTR), intent(in)   :: zmq_to_qp_run_socket
-  integer(ZMQ_PTR)               :: zmq_socket_pull
   integer, intent(in)            :: n_tasks, task_id(n_tasks)
-  integer, intent(in)            :: more
+  logical, intent(inout)         :: sending
   integer                        :: rc, k
   character*(64)                 :: fmt, reply
   character(LEN=:), allocatable  :: message
 
+  if (sending) then
+    print *,  irp_here, ': sending is true'
+    stop -1
+  endif
+  sending = .True.
   zmq_delete_tasks_async_send = 0
 
   allocate(character(LEN=64+n_tasks*12) :: message)
@@ -1162,7 +1222,7 @@ integer function zmq_delete_tasks_async_send(zmq_to_qp_run_socket,zmq_socket_pul
 end
 
 
-integer function zmq_delete_tasks_async_recv(zmq_to_qp_run_socket,zmq_socket_pull,task_id,n_tasks,more)
+integer function zmq_delete_tasks_async_recv(zmq_to_qp_run_socket,more,sending)
   use f77_zmq
   implicit none
   BEGIN_DOC
@@ -1170,12 +1230,12 @@ integer function zmq_delete_tasks_async_recv(zmq_to_qp_run_socket,zmq_socket_pul
 ! queue. This guarantees that the results have been received in the pull.
   END_DOC
   integer(ZMQ_PTR), intent(in)   :: zmq_to_qp_run_socket
-  integer(ZMQ_PTR)               :: zmq_socket_pull
-  integer, intent(in)            :: n_tasks, task_id(n_tasks)
   integer, intent(out)           :: more
+  logical, intent(inout)         :: sending
   integer                        :: rc
   character*(64)                 :: reply
 
+  if (.not.sending) return
   zmq_delete_tasks_async_recv = 0
 
   reply = ''
@@ -1188,6 +1248,7 @@ integer function zmq_delete_tasks_async_recv(zmq_to_qp_run_socket,zmq_socket_pul
   else
     zmq_delete_tasks_async_recv = -1
   endif
+  sending = .False.
 end