diff --git a/src/cipsi_tc_bi_ortho/fock_diag.irp.f b/src/cipsi_tc_bi_ortho/fock_diag.irp.f
new file mode 100644
index 00000000..af6849ab
--- /dev/null
+++ b/src/cipsi_tc_bi_ortho/fock_diag.irp.f
@@ -0,0 +1,95 @@
+subroutine build_fock_tmp_tc(fock_diag_tmp,det_ref,Nint)
+  use bitmasks
+  implicit none
+  BEGIN_DOC
+! Build the diagonal of the Fock matrix corresponding to a generator
+! determinant. $F_{00}$ is $\langle i|H|i \rangle = E_0$.
+  END_DOC
+  integer, intent(in)            :: Nint
+  integer(bit_kind), intent(in)  :: det_ref(Nint,2)
+  double precision, intent(out)  :: fock_diag_tmp(2,mo_num+1)
+
+  integer                        :: occ(Nint*bit_kind_size,2)
+  integer                        :: ne(2), i, j, ii, jj
+  double precision               :: E0
+
+  ! Compute Fock matrix diagonal elements
+  call bitstring_to_list_ab(det_ref,occ,Ne,Nint)
+
+  fock_diag_tmp = 0.d0
+  E0 = 0.d0
+
+  if (Ne(1) /= elec_alpha_num) then
+    print *,  'Error in build_fock_tmp_tc (alpha)', Ne(1), Ne(2)
+    call debug_det(det_ref,N_int)
+    stop -1
+  endif
+  if (Ne(2) /= elec_beta_num) then
+    print *, 'Error in build_fock_tmp_tc (beta)', Ne(1), Ne(2)
+    call debug_det(det_ref,N_int)
+    stop -1
+  endif
+
+  ! Occupied MOs
+  do ii=1,elec_alpha_num
+    i = occ(ii,1)
+    fock_diag_tmp(1,i) = fock_diag_tmp(1,i) + mo_one_e_integrals(i,i)
+    E0 = E0 + mo_one_e_integrals(i,i)
+    do jj=1,elec_alpha_num
+      j = occ(jj,1)
+      if (i==j) cycle
+      fock_diag_tmp(1,i) = fock_diag_tmp(1,i) + mo_two_e_integrals_jj_anti(i,j)
+      E0 = E0 + 0.5d0*mo_two_e_integrals_jj_anti(i,j)
+    enddo
+    do jj=1,elec_beta_num
+      j = occ(jj,2)
+      fock_diag_tmp(1,i) = fock_diag_tmp(1,i) + mo_two_e_integrals_jj(i,j)
+      E0 = E0 + mo_two_e_integrals_jj(i,j)
+    enddo
+  enddo
+  do ii=1,elec_beta_num
+    i = occ(ii,2)
+    fock_diag_tmp(2,i) = fock_diag_tmp(2,i) + mo_one_e_integrals(i,i)
+    E0 = E0 + mo_one_e_integrals(i,i)
+    do jj=1,elec_beta_num
+      j = occ(jj,2)
+      if (i==j) cycle
+      fock_diag_tmp(2,i) = fock_diag_tmp(2,i) + mo_two_e_integrals_jj_anti(i,j)
+      E0 = E0 + 0.5d0*mo_two_e_integrals_jj_anti(i,j)
+    enddo
+    do jj=1,elec_alpha_num
+      j = occ(jj,1)
+      fock_diag_tmp(2,i) = fock_diag_tmp(2,i) + mo_two_e_integrals_jj(i,j)
+    enddo
+  enddo
+
+  ! Virtual MOs
+  do i=1,mo_num
+    if (fock_diag_tmp(1,i) /= 0.d0) cycle
+    fock_diag_tmp(1,i) = fock_diag_tmp(1,i) + mo_one_e_integrals(i,i)
+    do jj=1,elec_alpha_num
+      j = occ(jj,1)
+      fock_diag_tmp(1,i) = fock_diag_tmp(1,i) + mo_two_e_integrals_jj_anti(i,j)
+    enddo
+    do jj=1,elec_beta_num
+      j = occ(jj,2)
+      fock_diag_tmp(1,i) = fock_diag_tmp(1,i) + mo_two_e_integrals_jj(i,j)
+    enddo
+  enddo
+  do i=1,mo_num
+    if (fock_diag_tmp(2,i) /= 0.d0) cycle
+    fock_diag_tmp(2,i) = fock_diag_tmp(2,i) + mo_one_e_integrals(i,i)
+    do jj=1,elec_beta_num
+      j = occ(jj,2)
+      fock_diag_tmp(2,i) = fock_diag_tmp(2,i) + mo_two_e_integrals_jj_anti(i,j)
+    enddo
+    do jj=1,elec_alpha_num
+      j = occ(jj,1)
+      fock_diag_tmp(2,i) = fock_diag_tmp(2,i) + mo_two_e_integrals_jj(i,j)
+    enddo
+  enddo
+
+  fock_diag_tmp(1,mo_num+1) = E0
+  fock_diag_tmp(2,mo_num+1) = E0
+
+end
diff --git a/src/cipsi_tc_bi_ortho/selection.irp.f b/src/cipsi_tc_bi_ortho/selection.irp.f
index 659e50a8..8137b922 100644
--- a/src/cipsi_tc_bi_ortho/selection.irp.f
+++ b/src/cipsi_tc_bi_ortho/selection.irp.f
@@ -19,7 +19,7 @@ subroutine select_connected(i_generator, E0, pt2_data, b, subset, csubset)
 
   allocate(fock_diag_tmp(2,mo_num+1))
 
-  call build_fock_tmp(fock_diag_tmp, psi_det_generators(1,1,i_generator), N_int)
+  call build_fock_tmp_tc(fock_diag_tmp, psi_det_generators(1,1,i_generator), N_int)
 
   do k = 1, N_int
       hole_mask(k,1)     = iand(generators_bitmask(k,1,s_hole), psi_det_generators(k,1,i_generator))