diff --git a/src/mo_two_e_ints/core_quantities.irp.f b/src/mo_two_e_ints/core_quantities.irp.f
index 1cc50cb1..349b0cd1 100644
--- a/src/mo_two_e_ints/core_quantities.irp.f
+++ b/src/mo_two_e_ints/core_quantities.irp.f
@@ -5,6 +5,16 @@ BEGIN_PROVIDER [double precision, core_energy]
  END_DOC
  integer :: i,j,k,l
  core_energy = 0.d0
+ if (is_periodic) then
+  do i = 1, n_core_orb
+   j = list_core(i)
+   core_energy += 2.d0 * dble(mo_one_e_integrals_complex(j,j)) + mo_two_e_integrals_jj(j,j)
+   do k = i+1, n_core_orb
+    l = list_core(k)
+    core_energy += 2.d0 * (2.d0 * mo_two_e_integrals_jj(j,l) - mo_two_e_integrals_jj_exchange(j,l))
+   enddo
+  enddo
+ else
  do i = 1, n_core_orb
   j = list_core(i)
   core_energy += 2.d0 * mo_one_e_integrals(j,j) + mo_two_e_integrals_jj(j,j)
@@ -13,6 +23,7 @@ BEGIN_PROVIDER [double precision, core_energy]
    core_energy += 2.d0 * (2.d0 * mo_two_e_integrals_jj(j,l) - mo_two_e_integrals_jj_exchange(j,l))
   enddo
  enddo
+ endif
  core_energy += nuclear_repulsion
 
 END_PROVIDER
@@ -36,3 +47,25 @@ BEGIN_PROVIDER [double precision, core_fock_operator, (mo_num,mo_num)]
   enddo
  enddo
 END_PROVIDER
+
+BEGIN_PROVIDER [complex*16, core_fock_operator_complex, (mo_num,mo_num)]
+ implicit none
+ integer :: i,j,k,l,m,n
+ complex*16 :: get_two_e_integral_periodic
+ BEGIN_DOC
+! this is the contribution to the Fock operator from the core electrons
+ END_DOC
+ core_fock_operator_complex = (0.d0,0.d0)
+ do i = 1, n_act_orb
+  j = list_act(i)
+  do k = 1, n_act_orb
+   l = list_act(k)
+   do m = 1, n_core_orb
+    n = list_core(m)
+    core_fock_operator_complex(j,l) += 2.d0 * &
+                    get_two_e_integral_periodic(j,n,l,n,mo_integrals_map,mo_integrals_map_2) - &
+                    get_two_e_integral_periodic(j,n,n,l,mo_integrals_map,mo_integrals_map_2)
+   enddo
+  enddo
+ enddo
+END_PROVIDER