diff --git a/src/davidson/diagonalize_ci.irp.f b/src/davidson/diagonalize_ci.irp.f
index 46ad8f78..6930cc07 100644
--- a/src/davidson/diagonalize_ci.irp.f
+++ b/src/davidson/diagonalize_ci.irp.f
@@ -1,3 +1,13 @@
+BEGIN_PROVIDER [ character*(3), sigma_vector_algorithm ]
+ implicit none
+ BEGIN_DOC
+ ! If 'det', use <Psi_det|H|Psi_det> in Davidson
+ !
+ ! If 'cfg', use <Psi_csf|H|Psi_csf> in Davidson
+ END_DOC
+ sigma_vector_algorithm = 'det'
+END_PROVIDER
+
 BEGIN_PROVIDER [ double precision, CI_energy, (N_states_diag) ]
   implicit none
   BEGIN_DOC
@@ -61,9 +71,18 @@ END_PROVIDER
    if (diag_algorithm == "Davidson") then
 
      if (do_csf) then
-       call davidson_diag_H_csf(psi_det,CI_eigenvectors, &
-         size(CI_eigenvectors,1),CI_electronic_energy,               &
-         N_det,N_csf,min(N_det,N_states),min(N_det,N_states_diag),N_int,0,converged)
+       if (sigma_vector_algorithm == 'det') then
+         call davidson_diag_H_csf(psi_det,CI_eigenvectors, &
+           size(CI_eigenvectors,1),CI_electronic_energy,               &
+           N_det,N_csf,min(N_det,N_states),min(N_det,N_states_diag),N_int,0,converged)
+!       else if (sigma_vector_algorithm == 'cfg') then
+!       call davidson_diag_H_csf(psi_det,CI_eigenvectors, &
+!         size(CI_eigenvectors,1),CI_electronic_energy,               &
+!         N_det,N_csf,min(N_det,N_states),min(N_det,N_states_diag),N_int,0,converged)
+!       else
+!         print *, irp_here
+!         stop 'bug'
+       endif
      else
        call davidson_diag_HS2(psi_det,CI_eigenvectors, CI_s2, &
          size(CI_eigenvectors,1),CI_electronic_energy,               &