diff --git a/src/casscf/swap_orb.irp.f b/src/casscf/swap_orb.irp.f
new file mode 100644
index 00000000..38e0f2e8
--- /dev/null
+++ b/src/casscf/swap_orb.irp.f
@@ -0,0 +1,70 @@
+ BEGIN_PROVIDER [double precision, super_ci_dm, (mo_num,mo_num)]
+ implicit none 
+ super_ci_dm = 0.d0
+ integer :: i,j
+ integer :: iorb,jorb
+ integer :: a,aorb
+ double precision :: c0,ci
+ c0 = SXeigenvec(1,1)
+ ! equation B3.a of the annex B of Roos et. al. Chemical Physics 48 (1980) 157-173
+ do i = 1, n_core_inact_orb
+  iorb = list_core_inact(i)
+  super_ci_dm(iorb,iorb) = 2.d0
+  do j = 1, n_core_inact_orb
+   jorb = list_core_inact(j)
+   ! loop over the core/inact 
+   do a = 1, n_virt_orb
+    aorb = list_virt(a)
+    super_ci_dm(jorb,iorb) += lowest_super_ci_coef_mo(aorb,iorb) * lowest_super_ci_coef_mo(aorb,jorb)
+   enddo
+  enddo
+ enddo
+
+ END_PROVIDER 
+ 
+ BEGIN_PROVIDER [double precision, lowest_super_ci_coef_mo, (mo_num,mo_num)]
+ implicit none
+ integer :: i,j,iorb,jorb
+ integer :: a, aorb,t, torb
+ double precision :: sqrt2
+
+ sqrt2 = 1.d0/dsqrt(2.d0)
+ do i = 1, nMonoEx
+  iorb = excit(1,i)
+  jorb = excit(2,i)
+  super_ci_coef_mo(iorb,jorb) = SXeigenvec(i+1,1)
+  super_ci_coef_mo(jorb,iorb) = SXeigenvec(i+1,1)
+ enddo
+
+ ! a_{ia} of the equation B.2 of Roos et. al. Chemical Physics 48 (1980) 157-173
+ do i = 1, n_core_inact_orb
+  iorb = list_core_inact(i)
+  do a = 1, n_virt_orb
+   aorb = list_virt(a)
+   super_ci_coef_mo(aorb,iorb) *= sqrt2
+   super_ci_coef_mo(iorb,aorb) *= sqrt2
+  enddo
+ enddo
+ 
+ ! a_{it} of the equation B.2 of Roos et. al. Chemical Physics 48 (1980) 157-173
+ do i = 1, n_core_inact_orb
+  iorb = list_core_inact(i)
+  do t = 1, n_act_orb
+   torb = list_act(t)
+   super_ci_coef_mo(torb,iorb) *= (2.d0 - occ_act(t))**(-0.5d0)
+   super_ci_coef_mo(iorb,torb) *= (2.d0 - occ_act(t))**(-0.5d0)
+  enddo
+ enddo
+
+ ! a_{ta} of the equation B.2 of Roos et. al. Chemical Physics 48 (1980) 157-173
+ do a = 1, n_virt_orb
+  aorb = list_virt(a)
+  do t = 1, n_act_orb
+   torb = list_act(t)
+   super_ci_coef_mo(torb,aorb) *= occ_act(t)**(-0.5d0)
+   super_ci_coef_mo(aorb,torb) *= occ_act(t)**(-0.5d0)
+  enddo
+ enddo
+
+ END_PROVIDER 
+