diff --git a/INSTALL.rst b/INSTALL.rst
index 34fbec57..7bcc114c 100644
--- a/INSTALL.rst
+++ b/INSTALL.rst
@@ -210,6 +210,12 @@ Zlib
    make
    make install
 
+With Debian or Ubuntu, you can use
+
+.. code:: bash
+
+   sudo apt install zlib1g-dev
+
 
 
 OCaml
@@ -217,6 +223,13 @@ OCaml
 
 *OCaml* is a general purpose programming language with an emphasis on expressiveness and safety.
 
+* The following packages are required (Debian or Ubuntu):
+
+  .. code:: bash
+
+    sudo apt install libncurses5-dev pkg-config libgmp3-dev m4
+
+
 * Download the installer of the OPAM package manager here :
   `<https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh>`_
   and move it in the :file:`${QP_ROOT}/external` directory
diff --git a/REPLACE b/REPLACE
index b23f324c..555616ac 100644
--- a/REPLACE
+++ b/REPLACE
@@ -183,3 +183,17 @@ qp_name save_one_body_dm -r save_one_e_dm
 qp_name ezfio_set_aux_quantities_data_one_e_alpha_dm_mo -r ezfio_set_aux_quantities_data_one_e_dm_alpha_mo
 qp_name ezfio_set_aux_quantities_data_one_e_beta_dm_mo -r ezfio_set_aux_quantities_data_one_e_dm_beta_mo
 qp_name two_electron_energy -r two_e_energy
+qp_name do_mono_excitation -r do_single_excitation
+qp_name get_mono_excitation -r get_single_excitation
+qp_name get_mono_excitation_from_fock -r get_single_excitation_from_fock
+qp_name is_connected_to_by_mono -r is_connected_to_by_single
+qp_name connected_to_ref_by_mono -r connected_to_ref_by_single
+qp_name mono_excitation_wee -r single_excitation_wee
+qp_name get_mono_excitation_spin
+qp_name get_mono_excitation_spin -r get_single_excitation_spin
+qp_name get_excitation_degree_vector_mono -r get_excitation_degree_vector_single
+qp_name get_excitation_degree_vector_mono_or_exchange -r get_excitation_degree_vector_single_or_exchange_or_exchange
+qp_name get_excitation_degree_vector_single_or_exchange_or_exchange -r get_excitation_degree_vector_single_or_exchange
+qp_name get_excitation_degree_vector_mono_or_exchange_verbose -r get_excitation_degree_vector_single_or_exchange_verbose
+qp_name i_h_j_mono_spin -r i_h_j_single_spin
+qp_name i_Wee_j_mono -r i_Wee_j_single
diff --git a/TODO b/TODO
index 699823ae..11be081c 100644
--- a/TODO
+++ b/TODO
@@ -49,8 +49,6 @@ Refaire les benchmarks
 # Documentation de qpsh
 
 # Documentation de /etc
-# Extrapolation qui prend aussi en compe la variance? a tester
-Parler dans le papier de rPT2
 
 # Toto
 Re-design de qp command
@@ -58,3 +56,5 @@ Re-design de qp command
 Doc: plugins et qp_plugins
 
 Ajouter les symetries dans devel
+
+Compiler ezfio avec openmp
diff --git a/configure b/configure
index 036594b1..5735563a 100755
--- a/configure
+++ b/configure
@@ -361,23 +361,24 @@ EOF
 
 
 done
-        
+
+source quantum_package.rc
 
 NINJA=$(find_exe ninja)
 if [[ ${NINJA} = $(not_found) ]] ; then
-        error "Ninja is not installed."
+        error "Ninja (ninja) is not installed."
         fail
 fi
 
 IRPF90=$(find_exe irpf90)
 if [[ ${IRPF90} = $(not_found) ]] ; then
-        error "IRPf90 is not installed."
+        error "IRPf90 (irpf90) is not installed."
         fail
 fi
 
 ZEROMQ=$(find_lib -lzmq)
 if [[ ${ZEROMQ} = $(not_found) ]] ; then
-        error "ZeroMQ is not installed."
+        error "ZeroMQ (zeromq) is not installed."
         fail
 fi
 
@@ -395,31 +396,31 @@ fi
 
 OCAML=$(find_exe ocaml)
 if [[ ${OCAML} = $(not_found) ]] ; then
-        error "OCaml compiler is not installed."
+        error "OCaml (ocaml) compiler is not installed."
         fail
 fi
 
 EZFIO=$(find_dir "${QP_ROOT}"/external/ezfio)
 if [[ ${EZFIO} = $(not_found) ]] ; then
-        error "EZFIO is not installed."
+        error "EZFIO (ezfio) is not installed."
         fail
 fi
 
 ZLIB=$(find_lib -lz)
 if [[ ${ZLIB} = $(not_found) ]] ; then
-        error "Zlib is not installed."
+        error "Zlib (zlib) is not installed."
         fail
 fi
 
 DOCOPT=$(find_python_lib docopt)
 if [[ ${DOCOPT} = $(not_found) ]] ; then
-        error "docopt is not installed."
+        error "docopt (docopt) is not installed."
         fail
 fi
 
 RESULTSFILE=$(find_python_lib resultsFile)
 if [[ ${RESULTSFILE} = $(not_found) ]] ; then
-        error "resultsFile is not installed."
+        error "resultsFile (resultsFile) is not installed."
         fail
 fi
 
diff --git a/src/cipsi/pt2_stoch_routines.irp.f b/src/cipsi/pt2_stoch_routines.irp.f
index 83924bb6..afa7a636 100644
--- a/src/cipsi/pt2_stoch_routines.irp.f
+++ b/src/cipsi/pt2_stoch_routines.irp.f
@@ -10,13 +10,20 @@ END_PROVIDER
 &BEGIN_PROVIDER [ integer, pt2_n_tasks_max ]
   implicit none
   logical, external :: testTeethBuilding
-  integer :: i
-  integer :: e
-  e = elec_num - n_core_orb * 2
-  pt2_n_tasks_max = 1+min((e*(e-1)), int(dsqrt(dble(N_det_selectors)))/10)
-  do i=1,N_det_generators
-    pt2_F(i) = 1 + int(dble(pt2_n_tasks_max)*dabs(maxval(psi_coef_sorted_gen(i,:)))**(0.75d0))
+  integer :: i,j
+  pt2_n_tasks_max = elec_beta_num*elec_beta_num + elec_alpha_num*elec_beta_num  - n_core_orb*2 
+  pt2_n_tasks_max = min(pt2_n_tasks_max,1+N_det_generators/10000)
+  call write_int(6,pt2_n_tasks_max,'pt2_n_tasks_max')
+
+  pt2_F(:) = int(sqrt(float(pt2_n_tasks_max)))
+  do i=1,pt2_n_0(1+pt2_N_teeth/4)
+    pt2_F(i) = pt2_n_tasks_max
   enddo
+  do i=1+pt2_n_0(pt2_N_teeth-pt2_N_teeth/4), N_det_generators
+    pt2_F(i) = 1
+  enddo
+
+
 END_PROVIDER
 
  BEGIN_PROVIDER [ integer, pt2_N_teeth ]
@@ -54,17 +61,16 @@ logical function testTeethBuilding(minF, N)
 
   allocate(tilde_w(N_det_generators), tilde_cW(0:N_det_generators))
 
-  do i=1,N_det_generators
-    tilde_w(i)  = psi_coef_sorted_gen(i,pt2_stoch_istate)**2 !+ 1.d-20
-  enddo
-
-  double precision :: norm
   norm = 0.d0
+  double precision :: norm
   do i=N_det_generators,1,-1
-    norm += tilde_w(i)
+    tilde_w(i)  = psi_coef_sorted_gen(i,pt2_stoch_istate) * &
+                  psi_coef_sorted_gen(i,pt2_stoch_istate)
+    norm = norm + tilde_w(i)
   enddo
 
-  tilde_w(:) = tilde_w(:) / norm
+  f = 1.d0/norm
+  tilde_w(:) = tilde_w(:) * f
 
   tilde_cW(0) = -1.d0
   do i=1,N_det_generators
@@ -74,10 +80,14 @@ logical function testTeethBuilding(minF, N)
 
   n0 = 0
   testTeethBuilding = .false.
+  double precision :: f
+  integer :: minFN
+  minFN = N_det_generators - minF * N
+  f = 1.d0/dble(N)
   do
     u0 = tilde_cW(n0)
     r = tilde_cW(n0 + minF)
-    Wt = (1d0 - u0) / dble(N)
+    Wt = (1d0 - u0) * f 
     if (dabs(Wt) <= 1.d-3) then
       return
     endif
@@ -86,7 +96,8 @@ logical function testTeethBuilding(minF, N)
        return
     end if
     n0 += 1
-    if(N_det_generators - n0 < minF * N) then
+!    if(N_det_generators - n0 < minF * N) then
+    if(n0 > minFN) then
       return
     end if
   end do
@@ -103,7 +114,6 @@ subroutine ZMQ_pt2(E, pt2,relative_error, error, variance, norm, N_in)
 
   integer(ZMQ_PTR)               :: zmq_to_qp_run_socket, zmq_socket_pull
   integer, intent(in)            :: N_in
-  integer, external              :: omp_get_thread_num
   double precision, intent(in)   :: relative_error, E(N_states)
   double precision, intent(out)  :: pt2(N_states),error(N_states)
   double precision, intent(out)  :: variance(N_states),norm(N_states)
@@ -111,7 +121,6 @@ subroutine ZMQ_pt2(E, pt2,relative_error, error, variance, norm, N_in)
 
   integer                        :: i, N
 
-  double precision, external     :: omp_get_wtime
   double precision               :: state_average_weight_save(N_states), w(N_states,4)
   integer(ZMQ_PTR), external     :: new_zmq_to_qp_run_socket
   type(selection_buffer)         :: b
@@ -120,9 +129,9 @@ subroutine ZMQ_pt2(E, pt2,relative_error, error, variance, norm, N_in)
   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
   PROVIDE psi_bilinear_matrix_transp_order psi_selectors_coef_transp psi_det_sorted
-  PROVIDE psi_det_hii
+  PROVIDE psi_det_hii N_generators_bitmask
 
-  if (s2_eig) then
+  if (h0_type == 'SOP') then
     PROVIDE psi_occ_pattern_hii det_to_occ_pattern
   endif
 
@@ -136,6 +145,10 @@ subroutine ZMQ_pt2(E, pt2,relative_error, error, variance, norm, N_in)
 
     N = max(N_in,1) * N_states
     state_average_weight_save(:) = state_average_weight(:)
+    if (int(N,8)*2_8 > huge(1)) then
+      print *,  irp_here, ': integer too large'
+      stop -1
+    endif
     call create_selection_buffer(N, N*2, b)
     ASSERT (associated(b%det))
     ASSERT (associated(b%val))
@@ -279,6 +292,7 @@ subroutine ZMQ_pt2(E, pt2,relative_error, error, variance, norm, N_in)
       print '(A)', ' Samples        Energy        Stat. Err     Variance          Norm          Seconds      '
       print '(A)', '========== ================= =========== =============== =============== ================='
 
+      PROVIDE global_selection_buffer 
       !$OMP PARALLEL DEFAULT(shared) NUM_THREADS(nproc_target+1)            &
           !$OMP  PRIVATE(i)
       i = omp_get_thread_num()
@@ -326,6 +340,7 @@ subroutine pt2_slave_inproc(i)
   implicit none
   integer, intent(in)            :: i
 
+  PROVIDE global_selection_buffer 
   call run_pt2_slave(1,i,pt2_e0_denominator)
 end
 
@@ -359,7 +374,6 @@ subroutine pt2_collector(zmq_socket_pull, E, relative_error, pt2, error, varianc
   integer, allocatable :: task_id(:)
   integer, allocatable :: index(:)
 
-  double precision, external :: omp_get_wtime
   double precision :: v, x, x2, x3, avg, avg2, avg3, eqt, E0, v0, n0
   double precision :: time, time1, time0
 
@@ -425,7 +439,6 @@ 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
@@ -478,6 +491,7 @@ subroutine pt2_collector(zmq_socket_pull, E, relative_error, pt2, error, varianc
         pt2(pt2_stoch_istate) = avg
         variance(pt2_stoch_istate) = avg2
         norm(pt2_stoch_istate) = avg3
+        call wall_time(time)
         ! 1/(N-1.5) : see  Brugger, The American Statistician (23) 4 p. 32 (1969)
         if(c > 2) then
           eqt = dabs((S2(t) / c) - (S(t)/c)**2) ! dabs for numerical stability
@@ -498,7 +512,6 @@ subroutine pt2_collector(zmq_socket_pull, E, relative_error, pt2, error, varianc
             endif
           endif
         endif
-        call wall_time(time)
       end if
       n += 1
     else if(more == 0) then
@@ -506,21 +519,21 @@ subroutine pt2_collector(zmq_socket_pull, E, relative_error, pt2, error, varianc
     else
       call pull_pt2_results(zmq_socket_pull, index, eI_task, vI_task, nI_task, task_id, n_tasks, b2)
       if (zmq_delete_tasks_async_send(zmq_to_qp_run_socket,task_id,n_tasks,sending) == -1) then
-          stop 'Unable to delete tasks'
+          stop 'PT2: Unable to delete tasks (send)'
       endif
       do i=1,n_tasks
-        eI(:, index(i)) += eI_task(:,i)
-        vI(:, index(i)) += vI_task(:,i)
-        nI(:, index(i)) += nI_task(:,i)
+        eI(1:N_states, index(i)) += eI_task(1:N_states,i)
+        vI(1:N_states, index(i)) += vI_task(1:N_states,i)
+        nI(1:N_states, index(i)) += nI_task(1:N_states,i)
         f(index(i)) -= 1
       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
+        call add_to_selection_buffer(b, b2%det(1,1,i), b2%val(i))
       end do
       if (zmq_delete_tasks_async_recv(zmq_to_qp_run_socket,more,sending) == -1) then
-          stop 'Unable to delete tasks'
+          stop 'PT2: Unable to delete tasks (recv)'
       endif
     end if
   end do
diff --git a/src/cipsi/run_pt2_slave.irp.f b/src/cipsi/run_pt2_slave.irp.f
index b4df2def..21def8f2 100644
--- a/src/cipsi/run_pt2_slave.irp.f
+++ b/src/cipsi/run_pt2_slave.irp.f
@@ -1,6 +1,46 @@
+ use omp_lib 
+ use selection_types
+ use f77_zmq
+BEGIN_PROVIDER [ integer(omp_lock_kind), global_selection_buffer_lock ]
+ use omp_lib 
+ implicit none
+ BEGIN_DOC
+ ! Global buffer for the OpenMP selection
+ END_DOC
+ call omp_init_lock(global_selection_buffer_lock)
+END_PROVIDER
+
+BEGIN_PROVIDER [ type(selection_buffer), global_selection_buffer ]
+ use omp_lib 
+ implicit none
+ BEGIN_DOC
+ ! Global buffer for the OpenMP selection
+ END_DOC
+ call omp_set_lock(global_selection_buffer_lock)
+ call delete_selection_buffer(global_selection_buffer)
+ call create_selection_buffer(N_det_generators, 2*N_det_generators, &
+    global_selection_buffer)
+ call omp_unset_lock(global_selection_buffer_lock)
+END_PROVIDER
+
+
 subroutine run_pt2_slave(thread,iproc,energy)
-  use f77_zmq
-  use selection_types
+ use selection_types
+ use f77_zmq
+  implicit none
+
+  double precision, intent(in)    :: energy(N_states_diag)
+  integer,  intent(in)            :: thread, iproc
+  if (N_det > nproc*(elec_alpha_num * (mo_num-elec_alpha_num))**2) then
+    call run_pt2_slave_large(thread,iproc,energy)
+  else
+    call run_pt2_slave_small(thread,iproc,energy)
+  endif
+end
+
+subroutine run_pt2_slave_small(thread,iproc,energy)
+ use selection_types
+ use f77_zmq
   implicit none
 
   double precision, intent(in)    :: energy(N_states_diag)
@@ -24,14 +64,9 @@ subroutine run_pt2_slave(thread,iproc,energy)
   integer :: n_tasks, k, N
   integer, allocatable :: i_generator(:), subset(:)
 
-  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)
+!  logical :: sending
 
   allocate(task_id(pt2_n_tasks_max), task(pt2_n_tasks_max))
   allocate(pt2(N_states,pt2_n_tasks_max), i_generator(pt2_n_tasks_max), subset(pt2_n_tasks_max))
@@ -52,9 +87,8 @@ subroutine run_pt2_slave(thread,iproc,energy)
   buffer_ready = .False.
   n_tasks = 1
 
-  sending = .False.
+!  sending = .False.
   done = .False.
-  n_tasks = 1
   do while (.not.done)
 
     n_tasks = max(1,n_tasks)
@@ -79,7 +113,130 @@ subroutine run_pt2_slave(thread,iproc,energy)
       call create_selection_buffer(bsize, bsize*2, b)
       buffer_ready = .True.
     else
-      ASSERT (N == b%N)
+      ASSERT (b%N == bsize)
+    endif
+
+    double precision :: time0, time1
+    call wall_time(time0)
+    do k=1,n_tasks
+        pt2(:,k) = 0.d0
+        variance(:,k) = 0.d0
+        norm(:,k) = 0.d0
+        b%cur = 0
+!double precision :: time2
+!call wall_time(time2)
+        call select_connected(i_generator(k),energy,pt2(1,k),variance(1,k),norm(1,k),b,subset(k),pt2_F(i_generator(k)))
+!call wall_time(time1)
+!print *,  i_generator(1), time1-time2, n_tasks, pt2_F(i_generator(1))
+    enddo
+    call wall_time(time1)
+!print *,  '-->', i_generator(1), time1-time0, n_tasks
+
+    integer, external :: tasks_done_to_taskserver
+    if (tasks_done_to_taskserver(zmq_to_qp_run_socket,worker_id,task_id,n_tasks) == -1) then
+      done = .true.
+    endif
+    call sort_selection_buffer(b)
+    call push_pt2_results(zmq_socket_push, i_generator, pt2, variance, norm, b, task_id, n_tasks)
+    b%cur=0
+
+!    ! 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)))
+    n_tasks = 1
+  end do
+
+  integer, external :: disconnect_from_taskserver
+  do i=1,300
+    if (disconnect_from_taskserver(zmq_to_qp_run_socket,worker_id) /= -2) exit
+    call sleep(1)
+    print *,  'Retry disconnect...'
+  end do
+
+  call end_zmq_push_socket(zmq_socket_push,thread)
+  call end_zmq_to_qp_run_socket(zmq_to_qp_run_socket)
+  if (buffer_ready) then
+    call delete_selection_buffer(b)
+  endif
+end subroutine
+
+
+subroutine run_pt2_slave_large(thread,iproc,energy)
+ use selection_types
+ use f77_zmq
+  implicit none
+
+  double precision, intent(in)    :: energy(N_states_diag)
+  integer,  intent(in)            :: thread, iproc
+  integer                         :: rc, i
+
+  integer                        :: worker_id, ctask, ltask
+  character*(512), allocatable   :: task(:)
+  integer, allocatable           :: task_id(:)
+
+  integer(ZMQ_PTR),external      :: new_zmq_to_qp_run_socket
+  integer(ZMQ_PTR)               :: zmq_to_qp_run_socket
+
+  integer(ZMQ_PTR), external     :: new_zmq_push_socket
+  integer(ZMQ_PTR)               :: zmq_socket_push
+
+  type(selection_buffer) :: b
+  logical :: done, buffer_ready
+
+  double precision,allocatable :: pt2(:,:), variance(:,:), norm(:,:)
+  integer :: n_tasks, k, N
+  integer, allocatable :: i_generator(:), subset(:)
+
+  integer :: bsize ! Size of selection buffers
+  logical :: sending
+  PROVIDE global_selection_buffer global_selection_buffer_lock
+
+
+  allocate(task_id(pt2_n_tasks_max), task(pt2_n_tasks_max))
+  allocate(pt2(N_states,pt2_n_tasks_max), i_generator(pt2_n_tasks_max), subset(pt2_n_tasks_max))
+  allocate(variance(N_states,pt2_n_tasks_max))
+  allocate(norm(N_states,pt2_n_tasks_max))
+
+  zmq_to_qp_run_socket = new_zmq_to_qp_run_socket()
+
+  integer, external :: connect_to_taskserver
+  if (connect_to_taskserver(zmq_to_qp_run_socket,worker_id,thread) == -1) then
+    call end_zmq_to_qp_run_socket(zmq_to_qp_run_socket)
+    return
+  endif
+
+  zmq_socket_push      = new_zmq_push_socket(thread)
+
+  b%N = 0
+  buffer_ready = .False.
+  n_tasks = 1
+
+  sending = .False.
+  done = .False.
+  do while (.not.done)
+
+    n_tasks = max(1,n_tasks)
+    n_tasks = min(pt2_n_tasks_max,n_tasks)
+
+    integer, external :: get_tasks_from_taskserver
+    if (get_tasks_from_taskserver(zmq_to_qp_run_socket,worker_id, task_id, task, n_tasks) == -1) then
+      exit
+    endif
+    done = task_id(n_tasks) == 0
+    if (done) then
+      n_tasks = n_tasks-1
+    endif
+    if (n_tasks == 0) exit
+
+    do k=1,n_tasks
+      read (task(k),*) subset(k), i_generator(k), N
+    enddo
+    if (b%N == 0) then
+      ! Only first time
+      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 (b%N == bsize)
     endif
 
     double precision :: time0, time1
@@ -104,11 +261,23 @@ subroutine run_pt2_slave(thread,iproc,energy)
     endif
     call sort_selection_buffer(b)
     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)
+    call omp_set_lock(global_selection_buffer_lock)
+    global_selection_buffer%mini = b%mini
+    call merge_selection_buffers(b,global_selection_buffer)
     b%cur=0
+    call omp_unset_lock(global_selection_buffer_lock)
+    if ( iproc == 1 ) then
+      call omp_set_lock(global_selection_buffer_lock)
+      call push_pt2_results_async_send(zmq_socket_push, i_generator, pt2, variance, norm, global_selection_buffer, task_id, n_tasks,sending)
+      global_selection_buffer%cur = 0
+      call omp_unset_lock(global_selection_buffer_lock)
+    else
+      call push_pt2_results_async_send(zmq_socket_push, i_generator, pt2, variance, norm, b, task_id, n_tasks,sending)
+    endif
 
-    ! 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)))
+!    ! 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)))
+    n_tasks = 1
   end do
   call push_pt2_results_async_recv(zmq_socket_push,b%mini,sending)
 
@@ -124,12 +293,13 @@ subroutine run_pt2_slave(thread,iproc,energy)
   if (buffer_ready) then
     call delete_selection_buffer(b)
   endif
+  FREE global_selection_buffer
 end subroutine
 
 
 subroutine push_pt2_results(zmq_socket_push, index, pt2, variance, norm, b, task_id, n_tasks)
-  use f77_zmq
-  use selection_types
+ use selection_types
+ use f77_zmq
   implicit none
 
   integer(ZMQ_PTR), intent(in)   :: zmq_socket_push
@@ -138,99 +308,17 @@ subroutine push_pt2_results(zmq_socket_push, index, pt2, variance, norm, b, task
   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
-  integer :: rc
-
-  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
-
-
-! 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
-IRP_ENDIF
 
+  logical :: sending
+  sending = .False.
+  call push_pt2_results_async_send(zmq_socket_push, index, pt2, variance, norm, b, task_id, n_tasks, sending)
+  call push_pt2_results_async_recv(zmq_socket_push, b%mini, sending)
 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
+ use selection_types
+ use f77_zmq
   implicit none
 
   integer(ZMQ_PTR), intent(in)   :: zmq_socket_push
@@ -241,6 +329,7 @@ subroutine push_pt2_results_async_send(zmq_socket_push, index, pt2, variance, no
   type(selection_buffer), intent(inout) :: b
   logical, intent(inout) :: sending
   integer :: rc
+  integer*8 :: rc8
 
   if (sending) then
     print *,  irp_here, ': sending is true'
@@ -250,6 +339,8 @@ subroutine push_pt2_results_async_send(zmq_socket_push, index, pt2, variance, no
 
   rc = f77_zmq_send( zmq_socket_push, n_tasks, 4, ZMQ_SNDMORE)
   if (rc == -1) then
+    print *,  irp_here, ': error sending result'
+    stop 1
     return
   else if(rc /= 4) then
     stop 'push'
@@ -258,6 +349,8 @@ subroutine push_pt2_results_async_send(zmq_socket_push, index, pt2, variance, no
 
   rc = f77_zmq_send( zmq_socket_push, index, 4*n_tasks, ZMQ_SNDMORE)
   if (rc == -1) then
+    print *,  irp_here, ': error sending result'
+    stop 2
     return
   else if(rc /= 4*n_tasks) then
     stop 'push'
@@ -266,6 +359,8 @@ subroutine push_pt2_results_async_send(zmq_socket_push, index, pt2, variance, no
 
   rc = f77_zmq_send( zmq_socket_push, pt2, 8*N_states*n_tasks, ZMQ_SNDMORE)
   if (rc == -1) then
+    print *,  irp_here, ': error sending result'
+    stop 3
     return
   else if(rc /= 8*N_states*n_tasks) then
     stop 'push'
@@ -274,6 +369,8 @@ subroutine push_pt2_results_async_send(zmq_socket_push, index, pt2, variance, no
 
   rc = f77_zmq_send( zmq_socket_push, variance, 8*N_states*n_tasks, ZMQ_SNDMORE)
   if (rc == -1) then
+    print *,  irp_here, ': error sending result'
+    stop 4
     return
   else if(rc /= 8*N_states*n_tasks) then
     stop 'push'
@@ -282,6 +379,8 @@ subroutine push_pt2_results_async_send(zmq_socket_push, index, pt2, variance, no
 
   rc = f77_zmq_send( zmq_socket_push, norm, 8*N_states*n_tasks, ZMQ_SNDMORE)
   if (rc == -1) then
+    print *,  irp_here, ': error sending result'
+    stop 5
     return
   else if(rc /= 8*N_states*n_tasks) then
     stop 'push'
@@ -290,40 +389,63 @@ subroutine push_pt2_results_async_send(zmq_socket_push, index, pt2, variance, no
 
   rc = f77_zmq_send( zmq_socket_push, task_id, n_tasks*4, ZMQ_SNDMORE)
   if (rc == -1) then
+    print *,  irp_here, ': error sending result'
+    stop 6
     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
+  if (b%cur == 0) then
+
+    rc = f77_zmq_send( zmq_socket_push, b%cur, 4, 0)
+    if (rc == -1) then
+      print *,  irp_here, ': error sending result'
+      stop 7
+      return
+    else if(rc /= 4) then
+      stop 'push'
+    endif
+
+  else
+
+    rc = f77_zmq_send( zmq_socket_push, b%cur, 4, ZMQ_SNDMORE)
+    if (rc == -1) then
+      print *,  irp_here, ': error sending result'
+      stop 7
+      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
+    rc8 = f77_zmq_send8( zmq_socket_push, b%val, 8_8*int(b%cur,8), ZMQ_SNDMORE)
+    if (rc8 == -1_8) then
+      print *,  irp_here, ': error sending result'
+      stop 8
+      return
+    else if(rc8 /= 8_8*int(b%cur,8)) 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'
+    rc8 = f77_zmq_send8( zmq_socket_push, b%det, int(bit_kind*N_int*2,8)*int(b%cur,8), 0)
+    if (rc8 == -1_8) then
+      print *,  irp_here, ': error sending result'
+      stop 9
+      return
+    else if(rc8 /= int(N_int*2*8,8)*int(b%cur,8)) then
+      stop 'push'
+    endif
+
   endif
 
 end subroutine
 
 subroutine push_pt2_results_async_recv(zmq_socket_push,mini,sending)
-  use f77_zmq
-  use selection_types
+ use selection_types
+ use f77_zmq
   implicit none
 
   integer(ZMQ_PTR), intent(in)    :: zmq_socket_push
@@ -339,12 +461,22 @@ IRP_ELSE
   character*(2) :: ok
   rc = f77_zmq_recv( zmq_socket_push, ok, 2, 0)
   if (rc == -1) then
+    print *,  irp_here, ': error sending result'
+    stop 10
     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)
+  if (rc == -1) then
+    print *,  irp_here, ': error sending result'
+    stop 11
+    return
+  else if (rc /= 8) then
+    print *,  irp_here//': error in receiving mini' 
+    stop 12
+  endif
 IRP_ENDIF
   sending = .False.
 end subroutine
@@ -352,8 +484,8 @@ end subroutine
 
 
 subroutine pull_pt2_results(zmq_socket_pull, index, pt2, variance, norm, task_id, n_tasks, b)
-  use f77_zmq
-  use selection_types
+ use selection_types
+ use f77_zmq
   implicit none
   integer(ZMQ_PTR), intent(in)   :: zmq_socket_pull
   double precision, intent(inout) :: pt2(N_states,*)
@@ -363,6 +495,7 @@ subroutine pull_pt2_results(zmq_socket_pull, index, pt2, variance, norm, task_id
   integer, intent(out) :: index(*)
   integer, intent(out) :: n_tasks, task_id(*)
   integer :: rc, rn, i
+  integer*8 :: rc8
 
   rc = f77_zmq_recv( zmq_socket_pull, n_tasks, 4, 0)
   if (rc == -1) then
@@ -420,22 +553,25 @@ subroutine pull_pt2_results(zmq_socket_pull, index, pt2, variance, norm, task_id
     stop 'pull'
   endif
 
-  rc = f77_zmq_recv( zmq_socket_pull, b%val, 8*b%cur, 0)
-  if (rc == -1) then
-    n_tasks = 1
-    task_id(1) = 0
-  else if(rc /= 8*b%cur) then
-    stop 'pull'
-  endif
+  if (b%cur > 0) then
 
-  rc = f77_zmq_recv( zmq_socket_pull, b%det, bit_kind*N_int*2*b%cur, 0)
-  if (rc == -1) then
-    n_tasks = 1
-    task_id(1) = 0
-  else if(rc /= N_int*2*8*b%cur) then
-    stop 'pull'
-  endif
+    rc8 = f77_zmq_recv8( zmq_socket_pull, b%val, 8_8*int(b%cur,8), 0)
+    if (rc8 == -1_8) then
+      n_tasks = 1
+      task_id(1) = 0
+    else if(rc8 /= 8_8*int(b%cur,8)) then
+      stop 'pull'
+    endif
 
+    rc8 = f77_zmq_recv8( zmq_socket_pull, b%det, int(bit_kind*N_int*2,8)*int(b%cur,8), 0)
+    if (rc8 == -1_8) then
+      n_tasks = 1
+      task_id(1) = 0
+    else if(rc8 /= int(N_int*2*8,8)*int(b%cur,8)) then
+      stop 'pull'
+    endif
+
+  endif
 
 ! Activate is zmq_socket_pull is a REP
 IRP_IF ZMQ_PUSH
diff --git a/src/cipsi/selection_buffer.irp.f b/src/cipsi/selection_buffer.irp.f
index 91fdcd3a..aa3be942 100644
--- a/src/cipsi/selection_buffer.irp.f
+++ b/src/cipsi/selection_buffer.irp.f
@@ -37,6 +37,11 @@ subroutine delete_selection_buffer(b)
   if (associated(b%val)) then
     deallocate(b%val)
   endif
+  NULLIFY(b%det)
+  NULLIFY(b%val)
+  b%cur = 0
+  b%mini = 0.d0
+  b%N = 0
 end
 
 
@@ -69,7 +74,7 @@ subroutine merge_selection_buffers(b1, b2)
   type(selection_buffer), intent(inout) :: b2
   integer(bit_kind), pointer     :: detmp(:,:,:)
   double precision, pointer      :: val(:)
-  integer                        :: i, i1, i2, k, nmwen
+  integer                        :: i, i1, i2, k, nmwen, sze
   if (b1%cur == 0) return
   do while (b1%val(b1%cur) > b2%mini)
     b1%cur = b1%cur-1
@@ -80,9 +85,10 @@ subroutine merge_selection_buffers(b1, b2)
   nmwen = min(b1%N, b1%cur+b2%cur)
   double precision :: rss
   double precision, external :: memory_of_double
-  rss = memory_of_double(size(b1%val)) + 2*N_int*memory_of_double(size(b1%det,3))
+  sze = max(size(b1%val), size(b2%val))
+  rss = memory_of_double(sze) + 2*N_int*memory_of_double(sze)
   call check_mem(rss,irp_here)
-  allocate( val(size(b1%val)), detmp(N_int, 2, size(b1%det,3)) )
+  allocate(val(sze), detmp(N_int, 2, sze))
   i1=1
   i2=1
   do i=1,nmwen
diff --git a/src/cipsi/slave_cipsi.irp.f b/src/cipsi/slave_cipsi.irp.f
index 0de07e67..58b53f94 100644
--- a/src/cipsi/slave_cipsi.irp.f
+++ b/src/cipsi/slave_cipsi.irp.f
@@ -232,6 +232,7 @@ subroutine run_slave_main
         endif
       IRP_ENDIF
 
+
       IRP_IF MPI_DEBUG
         call mpi_print('Entering OpenMP section')
       IRP_ENDIF
@@ -251,7 +252,7 @@ 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*ii+ ii)        & ! selection buffer
+                + 3.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
@@ -272,29 +273,37 @@ subroutine run_slave_main
           nproc_target = nproc_target - 1
 
         enddo
+        
+        if (N_det > 100000) then
 
-        if (mpi_master) then
-          print *,  'N_det', N_det
-          print *,  'N_det_generators', N_det_generators
-          print *,  'N_det_selectors', N_det_selectors
-          print *,  'pt2_e0_denominator', pt2_e0_denominator
-          print *,  'pt2_stoch_istate', pt2_stoch_istate
-          print *,  'state_average_weight', state_average_weight
-          print *,  'Number of threads', nproc_target
-          PROVIDE psi_det_hii
-
-          if (s2_eig) then
-            PROVIDE psi_occ_pattern_hii det_to_occ_pattern
+          if (mpi_master) then
+            print *,  'N_det', N_det
+            print *,  'N_det_generators', N_det_generators
+            print *,  'N_det_selectors', N_det_selectors
+            print *,  'pt2_e0_denominator', pt2_e0_denominator
+            print *,  'pt2_stoch_istate', pt2_stoch_istate
+            print *,  'state_average_weight', state_average_weight
+            print *,  'Number of threads', nproc_target
           endif
-        endif
 
-        !$OMP PARALLEL PRIVATE(i) NUM_THREADS(nproc_target+1)
-        i = omp_get_thread_num()
-        call run_pt2_slave(0,i,pt2_e0_denominator)
-        !$OMP END PARALLEL
+          if (h0_type == 'SOP') then
+            PROVIDE det_to_occ_pattern
+          endif
+
+          PROVIDE global_selection_buffer 
+          if (mpi_master) then
+            print *,  'Running PT2'
+          endif
+          !$OMP PARALLEL PRIVATE(i) NUM_THREADS(nproc_target+1)
+          i = omp_get_thread_num()
+          call run_pt2_slave(0,i,pt2_e0_denominator)
+          !$OMP END PARALLEL
+          FREE state_average_weight
+          print *,  mpi_rank, ': PT2 done'
+          print *,  '-------'
+
+        endif
       endif
-      FREE state_average_weight
-      print *,  mpi_rank, ': PT2 done'
 
       IRP_IF MPI
         call MPI_BARRIER(MPI_COMM_WORLD, ierr)
diff --git a/src/davidson/davidson_parallel.irp.f b/src/davidson/davidson_parallel.irp.f
index c615fae7..9e4402f6 100644
--- a/src/davidson/davidson_parallel.irp.f
+++ b/src/davidson/davidson_parallel.irp.f
@@ -359,7 +359,7 @@ subroutine davidson_collector(zmq_to_qp_run_socket, zmq_socket_pull, v0, s0, sze
   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'
+      stop 'davidson: Unable to delete task (send)'
     endif
     do j=1,N_st
       do i=imin,imax
@@ -368,7 +368,7 @@ subroutine davidson_collector(zmq_to_qp_run_socket, zmq_socket_pull, v0, s0, sze
       enddo
     enddo
     if (zmq_delete_task_async_recv(zmq_to_qp_run_socket,more,sending) == -1) then
-      stop 'Unable to delete task'
+      stop 'davidson: Unable to delete task (recv)'
     endif
   end do
   deallocate(v_t,s_t)
diff --git a/src/davidson/diagonalize_ci.irp.f b/src/davidson/diagonalize_ci.irp.f
index ab551084..d4b3b48c 100644
--- a/src/davidson/diagonalize_ci.irp.f
+++ b/src/davidson/diagonalize_ci.irp.f
@@ -202,6 +202,8 @@ subroutine diagonalize_CI
       psi_coef(i,j) = CI_eigenvectors(i,j)
     enddo
   enddo
+  psi_energy(1:N_states) = CI_electronic_energy(1:N_states)
+  psi_s2(1:N_states) = CI_s2(1:N_states)
 
-  SOFT_TOUCH psi_coef CI_electronic_energy CI_energy CI_eigenvectors CI_s2
+  SOFT_TOUCH psi_coef CI_electronic_energy CI_energy CI_eigenvectors CI_s2 psi_energy psi_s2
 end
diff --git a/src/davidson/u0_h_u0.irp.f b/src/davidson/u0_h_u0.irp.f
index c55cb631..726673ce 100644
--- a/src/davidson/u0_h_u0.irp.f
+++ b/src/davidson/u0_h_u0.irp.f
@@ -41,13 +41,27 @@ subroutine u_0_H_u_0(e_0,s_0,u_0,n,keys_tmp,Nint,N_st,sze)
 
   double precision, allocatable   :: v_0(:,:), s_vec(:,:), u_1(:,:)
   double precision                :: u_dot_u,u_dot_v,diag_H_mat_elem
-  integer                         :: i,j
+  integer                         :: i,j, istate
 
   if ((n > 100000).and.distributed_davidson) then
     allocate (v_0(n,N_states_diag),s_vec(n,N_states_diag), u_1(n,N_states_diag))
     u_1(:,:) = 0.d0
     u_1(1:n,1:N_st) = u_0(1:n,1:N_st)
     call H_S2_u_0_nstates_zmq(v_0,s_vec,u_1,N_states_diag,n)
+  else if (n < n_det_max_full) then
+    allocate (v_0(n,N_st),s_vec(n,N_st), u_1(n,N_st))
+    v_0(:,:) = 0.d0
+    u_1(:,:) = 0.d0
+    s_vec(:,:) = 0.d0
+    u_1(1:n,1:N_st) = u_0(1:n,1:N_st)
+    do istate = 1,N_st
+      do j=1,n
+        do i=1,n
+          v_0(i,istate) = v_0(i,istate) + h_matrix_all_dets(i,j) * u_0(j,istate)
+          s_vec(i,istate) = s_vec(i,istate) + S2_matrix_all_dets(i,j) * u_0(j,istate)
+        enddo
+      enddo
+    enddo
   else
     allocate (v_0(n,N_st),s_vec(n,N_st),u_1(n,N_st))
     u_1(:,:) = 0.d0
@@ -469,7 +483,7 @@ compute_singles=.True.
       ASSERT (lrow <= N_det_alpha_unique)
 
       tmp_det2(1:$N_int,1) = psi_det_alpha_unique(1:$N_int, lrow)
-      call i_H_j_mono_spin( tmp_det, tmp_det2, $N_int, 1, hij)
+      call i_h_j_single_spin( tmp_det, tmp_det2, $N_int, 1, hij)
 
       !DIR$ LOOP COUNT AVG(4)
       do l=1,N_st
@@ -554,7 +568,7 @@ compute_singles=.True.
       ASSERT (lcol <= N_det_beta_unique)
 
       tmp_det2(1:$N_int,2) = psi_det_beta_unique (1:$N_int, lcol)
-      call i_H_j_mono_spin( tmp_det, tmp_det2, $N_int, 2, hij)
+      call i_h_j_single_spin( tmp_det, tmp_det2, $N_int, 2, hij)
       l_a = psi_bilinear_matrix_transp_order(l_b)
       ASSERT (l_a <= N_det)
       !DIR$ LOOP COUNT AVG(4)
diff --git a/src/davidson/u0_wee_u0.irp.f b/src/davidson/u0_wee_u0.irp.f
index 1b16bfa1..c1f163d4 100644
--- a/src/davidson/u0_wee_u0.irp.f
+++ b/src/davidson/u0_wee_u0.irp.f
@@ -304,7 +304,7 @@ subroutine H_S2_u_0_two_e_nstates_openmp_work_$N_int(v_t,s_t,u_t,N_st,sze,istart
       ASSERT (lrow <= N_det_alpha_unique)
 
       tmp_det2(1:$N_int,1) = psi_det_alpha_unique(1:$N_int, lrow)
-      call i_Wee_j_mono( tmp_det, tmp_det2, $N_int, 1, hij)
+      call i_Wee_j_single( tmp_det, tmp_det2, $N_int, 1, hij)
 
       do l=1,N_st
         v_t(l,k_a) = v_t(l,k_a) + hij * u_t(l,l_a)
@@ -384,7 +384,7 @@ subroutine H_S2_u_0_two_e_nstates_openmp_work_$N_int(v_t,s_t,u_t,N_st,sze,istart
       ASSERT (lcol <= N_det_beta_unique)
 
       tmp_det2(1:$N_int,2) = psi_det_beta_unique (1:$N_int, lcol)
-      call i_Wee_j_mono( tmp_det, tmp_det2, $N_int, 2, hij)
+      call i_Wee_j_single( tmp_det, tmp_det2, $N_int, 2, hij)
       l_a = psi_bilinear_matrix_transp_order(l_b)
       ASSERT (l_a <= N_det)
       do l=1,N_st
diff --git a/src/determinants/connected_to_ref.irp.f b/src/determinants/connected_to_ref.irp.f
index c3760f69..086f19d1 100644
--- a/src/determinants/connected_to_ref.irp.f
+++ b/src/determinants/connected_to_ref.irp.f
@@ -185,7 +185,7 @@ end
 
 
 
-logical function is_connected_to_by_mono(key,keys,Nint,Ndet)
+logical function is_connected_to_by_single(key,keys,Nint,Ndet)
   use bitmasks
   implicit none
   BEGIN_DOC
@@ -202,7 +202,7 @@ logical function is_connected_to_by_mono(key,keys,Nint,Ndet)
   ASSERT (Nint > 0)
   ASSERT (Nint == N_int)
 
-  is_connected_to_by_mono = .false.
+  is_connected_to_by_single = .false.
 
   do i=1,Ndet
     degree_x2 = popcnt(xor( key(1,1), keys(1,1,i))) +              &
@@ -214,7 +214,7 @@ logical function is_connected_to_by_mono(key,keys,Nint,Ndet)
     if (degree_x2 > 2) then
       cycle
     else
-      is_connected_to_by_mono = .true.
+      is_connected_to_by_single = .true.
       return
     endif
   enddo
@@ -333,7 +333,7 @@ end
 
 
 
-integer function connected_to_ref_by_mono(key,keys,Nint,N_past_in,Ndet)
+integer function connected_to_ref_by_single(key,keys,Nint,N_past_in,Ndet)
   use bitmasks
   implicit none
   BEGIN_DOC
@@ -368,7 +368,7 @@ integer function connected_to_ref_by_mono(key,keys,Nint,N_past_in,Ndet)
   ASSERT (Nint > 0)
   ASSERT (Nint == N_int)
 
-  connected_to_ref_by_mono = 0
+  connected_to_ref_by_single = 0
   N_past = max(1,N_past_in)
   if (Nint == 1) then
 
@@ -380,7 +380,7 @@ integer function connected_to_ref_by_mono(key,keys,Nint,N_past_in,Ndet)
       else if (degree_x2 == 4)then
         cycle
       else if(degree_x2 == 2)then
-        connected_to_ref_by_mono = i
+        connected_to_ref_by_single = i
         return
       endif
     enddo
@@ -400,7 +400,7 @@ integer function connected_to_ref_by_mono(key,keys,Nint,N_past_in,Ndet)
       else if (degree_x2 == 4)then
         cycle
       else if(degree_x2 == 2)then
-        connected_to_ref_by_mono = i
+        connected_to_ref_by_single = i
         return
       endif
     enddo
@@ -421,7 +421,7 @@ integer function connected_to_ref_by_mono(key,keys,Nint,N_past_in,Ndet)
       else if (degree_x2 == 4)then
         cycle
       else if(degree_x2 == 2)then
-        connected_to_ref_by_mono = i
+        connected_to_ref_by_single = i
         return
       endif
     enddo
@@ -442,7 +442,7 @@ integer function connected_to_ref_by_mono(key,keys,Nint,N_past_in,Ndet)
       else if (degree_x2 == 4)then
         cycle
       else if(degree_x2 == 2)then
-        connected_to_ref_by_mono = i
+        connected_to_ref_by_single = i
         return
       endif
     enddo
diff --git a/src/determinants/create_excitations.irp.f b/src/determinants/create_excitations.irp.f
index d1bd0dd4..816006be 100644
--- a/src/determinants/create_excitations.irp.f
+++ b/src/determinants/create_excitations.irp.f
@@ -1,4 +1,4 @@
-subroutine do_mono_excitation(key_in,i_hole,i_particle,ispin,i_ok)
+subroutine do_single_excitation(key_in,i_hole,i_particle,ispin,i_ok)
   implicit none
   BEGIN_DOC
   ! Apply the single excitation operator : a^{dager}_(i_particle) a_(i_hole) of spin = ispin
diff --git a/src/determinants/density_matrix.irp.f b/src/determinants/density_matrix.irp.f
index bc5f45b5..a9630977 100644
--- a/src/determinants/density_matrix.irp.f
+++ b/src/determinants/density_matrix.irp.f
@@ -150,7 +150,7 @@ END_PROVIDER
       call get_excitation_degree_spin(tmp_det(1,1),tmp_det2,degree,N_int)
       if (degree == 1) then
         exc = 0
-        call get_mono_excitation_spin(tmp_det(1,1),tmp_det2,exc,phase,N_int)
+        call get_single_excitation_spin(tmp_det(1,1),tmp_det2,exc,phase,N_int)
         call decode_exc_spin(exc,h1,p1,h2,p2)
         do m=1,N_states
           ckl = psi_bilinear_matrix_values(k_a,m)*psi_bilinear_matrix_values(l,m) * phase
@@ -206,7 +206,7 @@ END_PROVIDER
       call get_excitation_degree_spin(tmp_det(1,2),tmp_det2,degree,N_int)
       if (degree == 1) then
         exc = 0
-        call get_mono_excitation_spin(tmp_det(1,2),tmp_det2,exc,phase,N_int)
+        call get_single_excitation_spin(tmp_det(1,2),tmp_det2,exc,phase,N_int)
         call decode_exc_spin(exc,h1,p1,h2,p2)
         do m=1,N_states
           ckl = psi_bilinear_matrix_transp_values(k_b,m)*psi_bilinear_matrix_transp_values(l,m) * phase
diff --git a/src/determinants/example.irp.f b/src/determinants/example.irp.f
index 97bc5388..4d5b6b55 100644
--- a/src/determinants/example.irp.f
+++ b/src/determinants/example.irp.f
@@ -29,7 +29,7 @@ subroutine example_determinants
   print*,'h1 --> p1 of spin s1'
   print*,'i_ok == +1 : excitation is possible '
   print*,'i_ok == -1 : excitation is NOT possible '
-  call do_mono_excitation(det_i,h1,p1,s1,i_ok)
+  call do_single_excitation(det_i,h1,p1,s1,i_ok)
   print*,'h1,p1,s1,i_ok'
   print*, h1,p1,s1,i_ok
   if(i_ok == -1)then
@@ -54,7 +54,7 @@ subroutine example_determinants
   h1 = elec_alpha_num
   p1 = elec_alpha_num + 1
   s1 = 2
-  call do_mono_excitation(det_i,h1,p1,s1,i_ok)
+  call do_single_excitation(det_i,h1,p1,s1,i_ok)
   print*,'h1,p1,s1,i_ok'
   print*, h1,p1,s1,i_ok
   call i_H_j(det_i,det_i,N_int,h0i)
diff --git a/src/determinants/h_apply.template.f b/src/determinants/h_apply.template.f
index 8149b664..169bd47e 100644
--- a/src/determinants/h_apply.template.f
+++ b/src/determinants/h_apply.template.f
@@ -236,7 +236,7 @@ subroutine $subroutine_diexcOrg(key_in,key_mask,hole_1,particl_1,hole_2, particl
       call bitstring_to_list_ab(particle_tmp,occ_particle_tmp,N_elec_in_key_part_2,N_int)
       call bitstring_to_list_ab(hole_tmp,occ_hole_tmp,N_elec_in_key_hole_2,N_int)
 
-      !   hole = a^(+)_j_a(ispin) a_i_a(ispin)|key_in> : mono exc :: orb(i_a,ispin) --> orb(j_a,ispin)
+      !   hole = a^(+)_j_a(ispin) a_i_a(ispin)|key_in> : single exc :: orb(i_a,ispin) --> orb(j_a,ispin)
       hole_save = hole
 
       ! Build array of the non-zero integrals of second excitation
@@ -297,7 +297,7 @@ subroutine $subroutine_diexcOrg(key_in,key_mask,hole_1,particl_1,hole_2, particl
         enddo
       endif
 
-      !   does all the mono excitations of the same spin
+      !   does all the single excitations of the same spin
       i=0
       do kk = 1,N_elec_in_key_hole_2(ispin)
         i_b = occ_hole_tmp(kk,ispin)
diff --git a/src/determinants/mono_excitations_bielec.irp.f b/src/determinants/single_excitation_two_e.irp.f
similarity index 96%
rename from src/determinants/mono_excitations_bielec.irp.f
rename to src/determinants/single_excitation_two_e.irp.f
index a4f46887..f150f531 100644
--- a/src/determinants/mono_excitations_bielec.irp.f
+++ b/src/determinants/single_excitation_two_e.irp.f
@@ -1,5 +1,5 @@
   use bitmasks
-subroutine mono_excitation_wee(det_1,det_2,h,p,spin,phase,hij)
+subroutine single_excitation_wee(det_1,det_2,h,p,spin,phase,hij)
  use bitmasks
  implicit none
  integer,intent(in) :: h,p,spin
@@ -79,7 +79,7 @@ BEGIN_PROVIDER [double precision, fock_wee_closed_shell, (mo_num, mo_num) ]
  enddo
  double precision :: array_coulomb(mo_num),array_exchange(mo_num)
  call bitstring_to_list_ab(key_virt, occ_virt, n_occ_ab_virt, N_int)
- ! docc ---> virt mono excitations
+ ! docc ---> virt single excitations
  do i0 = 1,  n_occ_ab(1)
   i=occ(i0,1)
   do j0 = 1, n_occ_ab_virt(1)
@@ -97,7 +97,7 @@ BEGIN_PROVIDER [double precision, fock_wee_closed_shell, (mo_num, mo_num) ]
   enddo
  enddo
 
- ! virt ---> virt mono excitations
+ ! virt ---> virt single excitations
  do i0 = 1,  n_occ_ab_virt(1)
   i=occ_virt(i0,1)
   do j0 = 1, n_occ_ab_virt(1)
@@ -114,7 +114,7 @@ BEGIN_PROVIDER [double precision, fock_wee_closed_shell, (mo_num, mo_num) ]
   enddo
  enddo
 
- ! docc ---> docc mono excitations
+ ! docc ---> docc single excitations
  do i0 = 1,  n_occ_ab(1)
   i=occ(i0,1)
   do j0 = 1, n_occ_ab(1)
diff --git a/src/determinants/single_excitations.irp.f b/src/determinants/single_excitations.irp.f
index 32b2dc0c..03ff0f7e 100644
--- a/src/determinants/single_excitations.irp.f
+++ b/src/determinants/single_excitations.irp.f
@@ -39,7 +39,7 @@ BEGIN_PROVIDER [double precision, fock_operator_closed_shell_ref_bitmask, (mo_nu
  double precision, allocatable :: array_coulomb(:),array_exchange(:)
  allocate (array_coulomb(mo_num),array_exchange(mo_num))
  call bitstring_to_list_ab(key_virt, occ_virt, n_occ_ab_virt, N_int)
- ! docc ---> virt mono excitations
+ ! docc ---> virt single excitations
  do i0 = 1,  n_occ_ab(1)
   i=occ(i0,1)
   do j0 = 1, n_occ_ab_virt(1)
@@ -57,7 +57,7 @@ BEGIN_PROVIDER [double precision, fock_operator_closed_shell_ref_bitmask, (mo_nu
   enddo
  enddo
 
- ! virt ---> virt mono excitations
+ ! virt ---> virt single excitations
  do i0 = 1,  n_occ_ab_virt(1)
   i=occ_virt(i0,1)
   do j0 = 1, n_occ_ab_virt(1)
@@ -74,7 +74,7 @@ BEGIN_PROVIDER [double precision, fock_operator_closed_shell_ref_bitmask, (mo_nu
   enddo
  enddo
 
- ! docc ---> docc mono excitations
+ ! docc ---> docc single excitations
  do i0 = 1,  n_occ_ab(1)
   i=occ(i0,1)
   do j0 = 1, n_occ_ab(1)
@@ -94,7 +94,7 @@ BEGIN_PROVIDER [double precision, fock_operator_closed_shell_ref_bitmask, (mo_nu
 
 END_PROVIDER
 
-subroutine get_mono_excitation_from_fock(det_1,det_2,h,p,spin,phase,hij)
+subroutine get_single_excitation_from_fock(det_1,det_2,h,p,spin,phase,hij)
  use bitmasks
  implicit none
  integer,intent(in) :: h,p,spin
diff --git a/src/determinants/slater_rules.irp.f b/src/determinants/slater_rules.irp.f
index a36d94a9..3f0f9335 100644
--- a/src/determinants/slater_rules.irp.f
+++ b/src/determinants/slater_rules.irp.f
@@ -93,7 +93,7 @@ subroutine get_excitation(det1,det2,exc,degree,phase,Nint)
       return
 
     case (1)
-      call get_mono_excitation(det1,det2,exc,phase,Nint)
+      call get_single_excitation(det1,det2,exc,phase,Nint)
       return
 
     case(0)
@@ -336,7 +336,7 @@ end
 
 
 
-subroutine get_mono_excitation(det1,det2,exc,phase,Nint)
+subroutine get_single_excitation(det1,det2,exc,phase,Nint)
   use bitmasks
   implicit none
   BEGIN_DOC
@@ -499,7 +499,7 @@ subroutine i_H_j_s2(key_i,key_j,Nint,hij,s2)
   select case (degree)
     case (2)
       call get_double_excitation(key_i,key_j,exc,phase,Nint)
-      ! Mono alpha, mono beta
+      ! Single alpha, single beta
       if (exc(0,1,1) == 1) then
         if ( (exc(1,1,1) == exc(1,2,2)).and.(exc(1,1,2) == exc(1,2,1)) ) then
           s2 =  -phase
@@ -541,21 +541,21 @@ subroutine i_H_j_s2(key_i,key_j,Nint,hij,s2)
             exc(1,2,2) ,mo_integrals_map) )
       endif
     case (1)
-      call get_mono_excitation(key_i,key_j,exc,phase,Nint)
+      call get_single_excitation(key_i,key_j,exc,phase,Nint)
       !DIR$ FORCEINLINE
       call bitstring_to_list_ab(key_i, occ, n_occ_ab, Nint)
-      ! Mono alpha
+      ! Single alpha
       if (exc(0,1,1) == 1) then
         m = exc(1,1,1)
         p = exc(1,2,1)
         spin = 1
-      ! Mono beta
+      ! Single beta
       else
         m = exc(1,1,2)
         p = exc(1,2,2)
         spin = 2
       endif
-      call get_mono_excitation_from_fock(key_i,key_j,p,m,spin,phase,hij)
+      call get_single_excitation_from_fock(key_i,key_j,p,m,spin,phase,hij)
 
     case (0)
       double precision, external :: diag_S_mat_elem
@@ -602,7 +602,7 @@ subroutine i_H_j(key_i,key_j,Nint,hij)
     case (2)
       call get_double_excitation(key_i,key_j,exc,phase,Nint)
       if (exc(0,1,1) == 1) then
-        ! Mono alpha, mono beta
+        ! Single alpha, single beta
         if(exc(1,1,1) == exc(1,2,2) )then
           hij = phase * big_array_exchange_integrals(exc(1,1,1),exc(1,1,2),exc(1,2,1))
         else if (exc(1,2,1) ==exc(1,1,2))then
@@ -640,21 +640,21 @@ subroutine i_H_j(key_i,key_j,Nint,hij)
             exc(1,2,2) ,mo_integrals_map) )
       endif
     case (1)
-      call get_mono_excitation(key_i,key_j,exc,phase,Nint)
+      call get_single_excitation(key_i,key_j,exc,phase,Nint)
       !DIR$ FORCEINLINE
       call bitstring_to_list_ab(key_i, occ, n_occ_ab, Nint)
       if (exc(0,1,1) == 1) then
-        ! Mono alpha
+        ! Single alpha
         m = exc(1,1,1)
         p = exc(1,2,1)
         spin = 1
       else
-        ! Mono beta
+        ! Single beta
         m = exc(1,1,2)
         p = exc(1,2,2)
         spin = 2
       endif
-      call get_mono_excitation_from_fock(key_i,key_j,p,m,spin,phase,hij)
+      call get_single_excitation_from_fock(key_i,key_j,p,m,spin,phase,hij)
 
     case (0)
       hij = diag_H_mat_elem(key_i,Nint)
@@ -703,7 +703,7 @@ subroutine i_H_j_verbose(key_i,key_j,Nint,hij,hmono,hdouble,phase)
     case (2)
       call get_double_excitation(key_i,key_j,exc,phase,Nint)
       if (exc(0,1,1) == 1) then
-        ! Mono alpha, mono beta
+        ! Single alpha, single beta
         hij = phase*get_two_e_integral(                          &
             exc(1,1,1),                                              &
             exc(1,1,2),                                              &
@@ -736,12 +736,12 @@ subroutine i_H_j_verbose(key_i,key_j,Nint,hij,hmono,hdouble,phase)
             exc(1,2,2) ,mo_integrals_map) )
       endif
     case (1)
-      call get_mono_excitation(key_i,key_j,exc,phase,Nint)
+      call get_single_excitation(key_i,key_j,exc,phase,Nint)
       !DIR$ FORCEINLINE
       call bitstring_to_list_ab(key_i, occ, n_occ_ab, Nint)
       has_mipi = .False.
       if (exc(0,1,1) == 1) then
-        ! Mono alpha
+        ! Single alpha
         m = exc(1,1,1)
         p = exc(1,2,1)
         do k = 1, elec_alpha_num
@@ -768,7 +768,7 @@ subroutine i_H_j_verbose(key_i,key_j,Nint,hij,hmono,hdouble,phase)
         enddo
 
       else
-        ! Mono beta
+        ! Single beta
         m = exc(1,1,2)
         p = exc(1,2,2)
         do k = 1, elec_beta_num
@@ -1060,7 +1060,7 @@ end
 
 
 
-subroutine get_excitation_degree_vector_mono(key1,key2,degree,Nint,sze,idx)
+subroutine get_excitation_degree_vector_single(key1,key2,degree,Nint,sze,idx)
   use bitmasks
   implicit none
   BEGIN_DOC
@@ -1154,7 +1154,7 @@ subroutine get_excitation_degree_vector_mono(key1,key2,degree,Nint,sze,idx)
 end
 
 
-subroutine get_excitation_degree_vector_mono_or_exchange(key1,key2,degree,Nint,sze,idx)
+subroutine get_excitation_degree_vector_single_or_exchange(key1,key2,degree,Nint,sze,idx)
   use bitmasks
   implicit none
   BEGIN_DOC
@@ -1202,7 +1202,7 @@ subroutine get_excitation_degree_vector_mono_or_exchange(key1,key2,degree,Nint,s
     enddo
   else
 
-    print*, 'get_excitation_degree_vector_mono_or_exchange not yet implemented for N_int > 1 ...'
+    print*, 'get_excitation_degree_vector_single_or_exchange not yet implemented for N_int > 1 ...'
     stop
 
   endif
@@ -1322,7 +1322,7 @@ subroutine get_excitation_degree_vector_double_alpha_beta(key1,key2,degree,Nint,
 end
 
 
-subroutine get_excitation_degree_vector_mono_or_exchange_verbose(key1,key2,degree,Nint,sze,idx)
+subroutine get_excitation_degree_vector_single_or_exchange_verbose(key1,key2,degree,Nint,sze,idx)
   use bitmasks
   implicit none
   BEGIN_DOC
@@ -1635,7 +1635,7 @@ double precision function diag_H_mat_elem_fock(det_ref,det_pert,fock_diag_tmp,Ni
     endif
 
   else if (degree == 1) then
-    call get_mono_excitation(det_ref,det_pert,exc,phase,Nint)
+    call get_single_excitation(det_ref,det_pert,exc,phase,Nint)
     call decode_exc(exc,1,h1,p1,h2,p2,s1,s2)
     if (s1 == 1) then
       diag_H_mat_elem_fock = E0 - fock_diag_tmp(1,h1) &
@@ -1775,7 +1775,17 @@ subroutine ac_operator(iorb,ispin,key,hjj,Nint,na,nb)
   integer                        :: other_spin
   integer                        :: k,l,i
 
-  ASSERT (iorb > 0)
+  if (iorb < 1) then
+    print *,  irp_here, 'iorb < 1'
+    print *,  iorb, mo_num
+    stop -1
+  endif
+  if (iorb > mo_num) then
+    print *,  irp_here, 'iorb > mo_num'
+    print *,  iorb, mo_num
+    stop -1
+  endif
+
   ASSERT (ispin > 0)
   ASSERT (ispin < 3)
   ASSERT (Nint > 0)
@@ -1793,11 +1803,6 @@ subroutine ac_operator(iorb,ispin,key,hjj,Nint,na,nb)
   key(k,ispin) = ibset(key(k,ispin),l)
   other_spin = iand(ispin,1)+1
 
-!  if (iorb > mo_num) then
-!    print *,  irp_here, 'iorb > mo_num'
-!    print *,  iorb, mo_num
-!    stop -1
-!  endif
   hjj = hjj + mo_one_e_integrals(iorb,iorb)
 
   ! Same spin
@@ -1921,7 +1926,7 @@ subroutine get_excitation_spin(det1,det2,exc,degree,phase,Nint)
       return
 
     case (1)
-      call get_mono_excitation_spin(det1,det2,exc,phase,Nint)
+      call get_single_excitation_spin(det1,det2,exc,phase,Nint)
       return
 
     case(0)
@@ -2093,7 +2098,7 @@ subroutine get_double_excitation_spin(det1,det2,exc,phase,Nint)
 
 end
 
-subroutine get_mono_excitation_spin(det1,det2,exc,phase,Nint)
+subroutine get_single_excitation_spin(det1,det2,exc,phase,Nint)
   use bitmasks
   implicit none
   BEGIN_DOC
@@ -2169,7 +2174,7 @@ subroutine get_mono_excitation_spin(det1,det2,exc,phase,Nint)
   enddo
 end
 
-subroutine i_H_j_mono_spin(key_i,key_j,Nint,spin,hij)
+subroutine i_H_j_single_spin(key_i,key_j,Nint,spin,hij)
   use bitmasks
   implicit none
   BEGIN_DOC
@@ -2185,8 +2190,8 @@ subroutine i_H_j_mono_spin(key_i,key_j,Nint,spin,hij)
 
   PROVIDE big_array_exchange_integrals mo_two_e_integrals_in_map
 
-  call get_mono_excitation_spin(key_i(1,spin),key_j(1,spin),exc,phase,Nint)
-  call get_mono_excitation_from_fock(key_i,key_j,exc(1,1),exc(1,2),spin,phase,hij)
+  call get_single_excitation_spin(key_i(1,spin),key_j(1,spin),exc,phase,Nint)
+  call get_single_excitation_from_fock(key_i,key_j,exc(1,1),exc(1,2),spin,phase,hij)
 end
 
 subroutine i_H_j_double_spin(key_i,key_j,Nint,hij)
@@ -2235,8 +2240,8 @@ subroutine i_H_j_double_alpha_beta(key_i,key_j,Nint,hij)
 
   PROVIDE big_array_exchange_integrals mo_two_e_integrals_in_map
 
-  call get_mono_excitation_spin(key_i(1,1),key_j(1,1),exc(0,1,1),phase,Nint)
-  call get_mono_excitation_spin(key_i(1,2),key_j(1,2),exc(0,1,2),phase2,Nint)
+  call get_single_excitation_spin(key_i(1,1),key_j(1,1),exc(0,1,1),phase,Nint)
+  call get_single_excitation_spin(key_i(1,2),key_j(1,2),exc(0,1,2),phase2,Nint)
   phase = phase*phase2
   if (exc(1,1,1) == exc(1,2,2)) then
     hij = phase * big_array_exchange_integrals(exc(1,1,1),exc(1,1,2),exc(1,2,1))
diff --git a/src/determinants/slater_rules_wee_mono.irp.f b/src/determinants/slater_rules_wee_mono.irp.f
index ce9b4b59..4c1c9330 100644
--- a/src/determinants/slater_rules_wee_mono.irp.f
+++ b/src/determinants/slater_rules_wee_mono.irp.f
@@ -1,5 +1,5 @@
 
-subroutine i_Wee_j_mono(key_i,key_j,Nint,spin,hij)
+subroutine i_Wee_j_single(key_i,key_j,Nint,spin,hij)
   use bitmasks
   implicit none
   BEGIN_DOC
@@ -15,8 +15,8 @@ subroutine i_Wee_j_mono(key_i,key_j,Nint,spin,hij)
 
   PROVIDE big_array_exchange_integrals mo_two_e_integrals_in_map
 
-  call get_mono_excitation_spin(key_i(1,spin),key_j(1,spin),exc,phase,Nint)
-  call mono_excitation_wee(key_i,key_j,exc(1,1),exc(1,2),spin,phase,hij)
+  call get_single_excitation_spin(key_i(1,spin),key_j(1,spin),exc,phase,Nint)
+  call single_excitation_wee(key_i,key_j,exc(1,1),exc(1,2),spin,phase,hij)
 end
 
 
@@ -188,7 +188,7 @@ subroutine i_H_j_mono_spin_one_e(key_i,key_j,Nint,spin,hij)
   integer                        :: exc(0:2,2)
   double precision               :: phase
 
-  call get_mono_excitation_spin(key_i(1,spin),key_j(1,spin),exc,phase,Nint)
+  call get_single_excitation_spin(key_i(1,spin),key_j(1,spin),exc,phase,Nint)
   integer :: m,p
   m = exc(1,1)
   p = exc(1,2)
@@ -252,7 +252,7 @@ subroutine i_H_j_one_e(key_i,key_j,Nint,hij)
   if(degree==0)then
    hij = diag_H_mat_elem_one_e(key_i,N_int)
   else
-   call get_mono_excitation(key_i,key_j,exc,phase,Nint)
+   call get_single_excitation(key_i,key_j,exc,phase,Nint)
    if (exc(0,1,1) == 1) then
      ! Mono alpha
      m = exc(1,1,1)
@@ -340,7 +340,7 @@ subroutine i_H_j_two_e(key_i,key_j,Nint,hij)
             exc(1,2,2) ,mo_integrals_map) )
       endif
     case (1)
-      call get_mono_excitation(key_i,key_j,exc,phase,Nint)
+      call get_single_excitation(key_i,key_j,exc,phase,Nint)
       !DIR$ FORCEINLINE
       call bitstring_to_list_ab(key_i, occ, n_occ_ab, Nint)
       if (exc(0,1,1) == 1) then
@@ -354,7 +354,7 @@ subroutine i_H_j_two_e(key_i,key_j,Nint,hij)
         p = exc(1,2,2)
         spin = 2
       endif
-      call mono_excitation_wee(key_i,key_j,p,m,spin,phase,hij)
+      call single_excitation_wee(key_i,key_j,p,m,spin,phase,hij)
     case (0)
       double precision :: diag_wee_mat_elem
       hij = diag_wee_mat_elem(key_i,Nint)
diff --git a/src/fci/40.fci.bats b/src/fci/40.fci.bats
index 645e7549..3d6a4858 100644
--- a/src/fci/40.fci.bats
+++ b/src/fci/40.fci.bats
@@ -18,8 +18,27 @@ function run() {
 }
 
 
+function run_stoch() {
+  thresh=$2
+  test_exe fci || skip
+  qp set perturbation do_pt2 True
+  qp set determinants n_det_max 100000
+  qp set determinants n_states  1
+  qp set davidson threshold_davidson 1.e-10
+  qp set davidson n_states_diag 1
+  qp run fci 
+  energy1="$(ezfio get fci energy_pt2 | tr '[]' ' ' | cut -d ',' -f 1)"
+  eq $energy1 $1 $thresh
+}
 
 
+@test "F2" { # 4.07m
+  [[ -n $TRAVIS ]] && skip
+  qp set_file f2.ezfio
+  qp set_frozen_core
+  run_stoch -199.30496 1.e-4
+}
+
 @test "NH3" { # 10.6657s
   qp set_file nh3.ezfio
   qp set_mo_class --core="[1-4]" --act="[5-72]"
@@ -34,13 +53,13 @@ function run() {
 
 @test "HCO" { # 12.2868s
   qp set_file hco.ezfio
-  run -113.296806579881 1.e-05 
+  run -113.296794171915 2.e-05 
 }
 
 @test "H2O2" { # 12.9214s
   qp set_file h2o2.ezfio
   qp set_mo_class --core="[1-2]" --act="[3-24]" --del="[25-38]"
-  run -151.004935161155 1.e-5
+  run -151.004888189874 2.e-5
 }
 
 @test "HBO" { # 13.3144s
@@ -52,19 +71,19 @@ function run() {
 @test "H2O" { # 11.3727s
   [[ -n $TRAVIS ]] && skip
   qp set_file h2o.ezfio
-  run -76.2359268957699 1.e-5
+  run -76.2359268957699 2.e-5
 }
 
 @test "ClO" { # 13.3755s
   [[ -n $TRAVIS ]] && skip
   qp set_file clo.ezfio
-  run -534.546053053143 1.e-5
+  run -534.546005867797 5.e-5
 }
 
 @test "SO" { # 13.4952s
   [[ -n $TRAVIS ]] && skip
   qp set_file so.ezfio
-  run -26.0126370436611 1.e-5
+  run -26.0144622194831 1.e-5
 }
 
 @test "H2S" { # 13.6745s
@@ -94,20 +113,20 @@ function run() {
 @test "SiH3" { # 15.99s
   [[ -n $TRAVIS ]] && skip
   qp set_file sih3.ezfio
-  run -5.57267383364177 1.e-05 
+  run -5.57269434557089 2.e-05 
 }
 
 @test "CH4" { # 16.1612s
   [[ -n $TRAVIS ]] && skip
   qp set_file ch4.ezfio
   qp set_mo_class --core="[1]" --act="[2-30]" --del="[31-59]"
-  run -40.2409672510721 1.e-5
+  run -40.2409858175829 2.e-5
 }
 
 @test "ClF" { # 16.8864s
   [[ -n $TRAVIS ]] && skip
   qp set_file clf.ezfio
-  run -559.168731496312 1.e-5
+  run -559.170116079903 1.e-5
 }
 
 @test "SO2" { # 17.5645s
@@ -121,36 +140,30 @@ function run() {
   [[ -n $TRAVIS ]] && skip
   qp set_file c2h2.ezfio
   qp set_mo_class --act="[1-30]" --del="[31-36]"
-  run -12.3671467643742 1.e-5
+  run -12.3678973551285 2.e-5
 }
 
 @test "N2" { # 18.0198s
   [[ -n $TRAVIS ]] && skip
   qp set_file n2.ezfio
   qp set_mo_class --core="[1,2]" --act="[3-40]" --del="[41-60]"
-  run -109.291382745482 1.e-5
+  run -109.291310557766 1.e-4
 }
 
 @test "N2H4" { # 18.5006s
   [[ -n $TRAVIS ]] && skip
   qp set_file n2h4.ezfio
   qp set_mo_class --core="[1-2]" --act="[3-24]" --del="[25-48]"
-  run -111.367234092521 1.e-5
+  run -111.367234092521 2.e-5
 }
 
 @test "CO2" { # 21.1748s
   [[ -n $TRAVIS ]] && skip
   qp set_file co2.ezfio
   qp set_mo_class --core="[1,2]" --act="[3-30]" --del="[31-42]"
-  run -187.969721107603 1.e-5
+  run -187.969556614801 1.e-5
 }
 
-@test "F2" { # 21.331s
-  [[ -n $TRAVIS ]] && skip
-  qp set_file f2.ezfio
-  qp set_mo_class --core="[1,2]" --act="[3-30]" --del="[31-62]"
-  run -199.068518708366 1.e-5 
-}
 
 @test "[Cu(NH3)4]2+" { # 25.0417s
   [[ -n $TRAVIS ]] && skip
@@ -163,6 +176,6 @@ function run() {
   [[ -n $TRAVIS ]] && skip
   qp set_file hcn.ezfio
   qp set_mo_class --core="[1,2]" --act="[3-40]" --del="[41-55]"
-  run -93.0779744802522 1.e-5
+  run -93.0794109423741 2.e-5
 }
 
diff --git a/src/mo_one_e_ints/mo_one_e_ints.irp.f b/src/mo_one_e_ints/mo_one_e_ints.irp.f
index 88a40f24..ac4b4e3b 100644
--- a/src/mo_one_e_ints/mo_one_e_ints.irp.f
+++ b/src/mo_one_e_ints/mo_one_e_ints.irp.f
@@ -2,10 +2,10 @@ BEGIN_PROVIDER [ double precision, mo_one_e_integrals,(mo_num,mo_num)]
   implicit none
   integer                        :: i,j,n,l
   BEGIN_DOC
-  ! array of the mono electronic hamiltonian on the MOs basis :
-  ! sum of the kinetic and nuclear electronic potential (and pseudo potential if needed)
+  ! array of the one-electron Hamiltonian on the |MO| basis :
+  ! sum of the kinetic and nuclear electronic potentials (and pseudo potential if needed)
   END_DOC
-  print*,'Providing the mono electronic integrals'
+  print*,'Providing the one-electron integrals'
 
   IF (read_mo_one_e_integrals) THEN
         call ezfio_get_mo_one_e_ints_mo_one_e_integrals(mo_one_e_integrals)
diff --git a/src/perturbation/EZFIO.cfg b/src/perturbation/EZFIO.cfg
index ab9cfc1a..b90a8961 100644
--- a/src/perturbation/EZFIO.cfg
+++ b/src/perturbation/EZFIO.cfg
@@ -22,4 +22,8 @@ doc: The selection process stops at a fixed correlation ratio (useful for gettin
 interface: ezfio,provider,ocaml
 default: 1.00
 
-
+[h0_type]
+type: character*(32)
+doc: Type of denominator in PT2. [EN | SOP | HF]
+interface: ezfio,provider,ocaml
+default: EN
diff --git a/src/perturbation/h0_type.irp.f b/src/perturbation/h0_type.irp.f
deleted file mode 100644
index 7dd58c2c..00000000
--- a/src/perturbation/h0_type.irp.f
+++ /dev/null
@@ -1,13 +0,0 @@
-BEGIN_PROVIDER [ character*32,h0_type ]
- implicit none
- BEGIN_DOC
- ! Type of zeroth-order Hamiltonian
- END_DOC
- if (s2_eig) then
-   h0_type = 'SOP'
- else
-   h0_type = 'EN'
- endif
-!   h0_type = 'HF'
-END_PROVIDER
-
diff --git a/src/perturbation/perturbation.template.f b/src/perturbation/perturbation.template.f
index 88c2160a..0a7ca181 100644
--- a/src/perturbation/perturbation.template.f
+++ b/src/perturbation/perturbation.template.f
@@ -198,7 +198,7 @@ subroutine perturb_buffer_by_mono_$PERT(i_generator,buffer,buffer_size,e_2_pert_
   double precision, intent(inout) :: coef_pert_buffer(N_st,buffer_size),e_2_pert_buffer(N_st,buffer_size),sum_H_pert_diag(N_st)
   double precision               :: c_pert(N_st), e_2_pert(N_st),  H_pert_diag(N_st)
   integer                        :: i,k, c_ref, ni, ex
-  integer, external              :: connected_to_ref_by_mono
+  integer, external              :: connected_to_ref_by_single
   logical, external              :: is_in_wavefunction
 
   integer(bit_kind), allocatable :: minilist(:,:,:)
@@ -232,7 +232,7 @@ subroutine perturb_buffer_by_mono_$PERT(i_generator,buffer,buffer_size,e_2_pert_
 
   do i=1,buffer_size
 
-    c_ref = connected_to_ref_by_mono(buffer(1,1,i),psi_det_generators,Nint,i_generator,N_det)
+    c_ref = connected_to_ref_by_single(buffer(1,1,i),psi_det_generators,Nint,i_generator,N_det)
 
     if (c_ref /= 0) then
       cycle
diff --git a/src/zmq/utils.irp.f b/src/zmq/utils.irp.f
index 4c838302..1205e09e 100644
--- a/src/zmq/utils.irp.f
+++ b/src/zmq/utils.irp.f
@@ -604,11 +604,11 @@ subroutine end_parallel_job(zmq_to_qp_run_socket,zmq_socket_pull,name_in)
     rc = f77_zmq_send(zmq_to_qp_run_socket, 'end_job '//trim(zmq_state),8+len(trim(zmq_state)),0)
     rc = f77_zmq_recv(zmq_to_qp_run_socket, message, 512, 0)
     if (trim(message(1:13)) == 'error waiting') then
-      call sleep(1)
       cycle
     else if (message(1:2) == 'ok') then
       exit
     endif
+    call sleep(1)
   end do
   if (i==0) then
     print *,  '.. Forcing kill ..'
@@ -1127,6 +1127,7 @@ integer function zmq_delete_task_async_recv(zmq_to_qp_run_socket,more,sending)
   integer                        :: rc
   character*(512)                :: message
   character*(64) :: reply
+  zmq_delete_task_async_recv = 0
   if (.not.sending) return
   sending = .False.
   reply = ''
@@ -1136,6 +1137,7 @@ integer function zmq_delete_task_async_recv(zmq_to_qp_run_socket,more,sending)
   else if (reply(16:19) == 'done') then
     more = 0
   else
+    print *,  reply(1:rc)
     zmq_delete_task_async_recv = -1
     return
   endif