diff --git a/src/Dets/psi_cas.irp.f b/src/Dets/psi_cas.irp.f
new file mode 100644
index 00000000..299e5e8f
--- /dev/null
+++ b/src/Dets/psi_cas.irp.f
@@ -0,0 +1,114 @@
+use bitmasks
+
+ BEGIN_PROVIDER [ integer(bit_kind), psi_cas, (N_int,2,psi_det_size) ]
+&BEGIN_PROVIDER [ double precision, psi_cas_coef,  (psi_det_size,n_states) ]
+&BEGIN_PROVIDER [ integer, idx_cas, (psi_det_size) ]
+&BEGIN_PROVIDER [ integer, N_det_cas ]
+  implicit none
+  BEGIN_DOC
+  ! CAS wave function, defined from the application of the CAS bitmask on the 
+  ! determinants. idx_cas gives the indice of the CAS determinant in psi_det.
+  END_DOC
+  integer                        :: i, k, l
+  logical                        :: good
+  N_det_cas = 0
+  do i=1,N_det
+    do l=1,n_cas_bitmask
+      good = .True.
+      do k=1,N_int
+        good = good .and. (                                          &
+            iand(not(cas_bitmask(k,1,l)), psi_det(k,1,i)) ==         &
+            iand(not(cas_bitmask(k,1,l)), psi_det(k,1,1)) ) .and. (  &
+            iand(not(cas_bitmask(k,2,l)), psi_det(k,2,i)) ==         &
+            iand(not(cas_bitmask(k,2,l)), psi_det(k,2,1)) )
+      enddo
+      if (good) then
+        exit
+      endif
+    enddo
+    if (good) then
+      N_det_cas = N_det_cas+1
+      do k=1,N_int
+        psi_cas(k,1,N_det_cas) = psi_det(k,1,i)
+        psi_cas(k,2,N_det_cas) = psi_det(k,2,i)
+      enddo
+      idx_cas(N_det_cas) = i
+      do k=1,N_states
+        psi_cas_coef(N_det_cas,k) = psi_coef(i,k)
+      enddo
+    endif
+  enddo
+  call write_int(output_dets,N_det_cas, 'Number of determinants in the CAS')
+
+END_PROVIDER
+
+
+ BEGIN_PROVIDER [ integer(bit_kind), psi_cas_sorted_bit, (N_int,2,psi_det_size) ]
+&BEGIN_PROVIDER [ double precision, psi_cas_coef_sorted_bit, (psi_det_size,N_states) ]
+ implicit none
+ BEGIN_DOC
+ ! CAS determinants sorted to accelerate the search of a random determinant in the wave
+ ! function.
+ END_DOC
+ call sort_dets_by_det_search_key(N_det_cas, psi_cas, psi_cas_coef, &
+     psi_cas_sorted_bit, psi_cas_coef_sorted_bit)
+
+END_PROVIDER
+
+
+
+ BEGIN_PROVIDER [ integer(bit_kind), psi_non_cas,  (N_int,2,psi_det_size) ]
+&BEGIN_PROVIDER [ double precision, psi_non_cas_coef, (psi_det_size,n_states) ]
+&BEGIN_PROVIDER [ integer, idx_non_cas,  (psi_det_size) ]
+&BEGIN_PROVIDER [ integer, N_det_non_cas ]
+ implicit none
+ BEGIN_DOC
+  ! Set of determinants which are not part of the CAS, defined from the application
+  ! of the CAS bitmask on the determinants. 
+  ! idx_non_cas gives the indice of the determinant in psi_det.
+ END_DOC
+ integer                        :: i_non_cas,j,k
+ integer                        :: degree
+ logical                        :: in_cas
+ i_non_cas =0
+ do k=1,N_det
+   in_cas = .False.
+   do j=1,N_det_cas
+     call get_excitation_degree(psi_cas(1,1,j), psi_det(1,1,k), degree, N_int)
+     if (degree == 0) then
+       in_cas = .True.
+       exit
+     endif
+   enddo
+   if (.not.in_cas) then
+     double precision :: hij
+     i_non_cas += 1
+     do j=1,N_int
+       psi_non_cas(j,1,i_non_cas) = psi_det(j,1,k)
+       psi_non_cas(j,2,i_non_cas) = psi_det(j,2,k)
+     enddo
+     do j=1,N_states
+       psi_non_cas_coef(i_non_cas,j) = psi_coef(k,j)
+     enddo
+     idx_non_cas(i_non_cas) = k
+   endif
+ enddo
+ N_det_non_cas = i_non_cas
+END_PROVIDER
+
+ BEGIN_PROVIDER [ integer(bit_kind), psi_non_cas_sorted_bit, (N_int,2,psi_det_size) ]
+&BEGIN_PROVIDER [ double precision, psi_non_cas_coef_sorted_bit, (psi_det_size,N_states) ]
+ implicit none
+ BEGIN_DOC
+ ! CAS determinants sorted to accelerate the search of a random determinant in the wave
+ ! function.
+ END_DOC
+ call sort_dets_by_det_search_key(N_det_cas, psi_non_cas, psi_non_cas_coef, &
+     psi_non_cas_sorted_bit, psi_non_cas_coef_sorted_bit)
+
+END_PROVIDER
+
+
+
+
+