diff --git a/src/MOGuess/mo_ortho_lowdin.irp.f b/src/MOGuess/mo_ortho_lowdin.irp.f
index 99063da2..c73bb553 100644
--- a/src/MOGuess/mo_ortho_lowdin.irp.f
+++ b/src/MOGuess/mo_ortho_lowdin.irp.f
@@ -1,46 +1,50 @@
 
 BEGIN_PROVIDER [double precision, ao_ortho_lowdin_coef, (ao_num_align,ao_num)]
- BEGIN_DOC
+  implicit none
+  BEGIN_DOC
 ! matrix of the coefficients of the mos generated by the 
 ! orthonormalization by the S^{-1/2} canonical transformation of the aos
 ! ao_ortho_lowdin_coef(i,j) = coefficient of the ith ao on the jth ao_ortho_lowdin orbital
- END_DOC
- implicit none
- integer :: i,j,k,l
- double precision :: tmp_matrix(ao_num_align,ao_num),accu
- do i = 1, ao_num
-  do j = 1, ao_num
-   tmp_matrix(i,j) = 0.d0
+  END_DOC
+  integer                        :: i,j,k,l
+  double precision               :: tmp_matrix(ao_num_align,ao_num),accu
+  do j=1, ao_num
+    do i=1, ao_num
+      tmp_matrix(i,j) = 0.d0
+    enddo
   enddo
- enddo
- do i = 1, ao_num
-  tmp_matrix(i,i) = 1.d0
- enddo
- call ortho_lowdin(ao_overlap,ao_num_align,ao_num,tmp_matrix,ao_num_align,ao_num)
- do i = 1, ao_num
-  do j = 1, ao_num
-   ao_ortho_lowdin_coef(j,i) = tmp_matrix(i,j)
+  do i=1, ao_num
+    tmp_matrix(i,i) = 1.d0
+  enddo
+  call ortho_lowdin(ao_overlap,ao_num_align,ao_num,tmp_matrix,ao_num_align,ao_num)
+  do i=1, ao_num
+    do j=1, ao_num
+      ao_ortho_lowdin_coef(j,i) = tmp_matrix(i,j)
+    enddo
   enddo
- enddo
 END_PROVIDER
 BEGIN_PROVIDER [double precision, ao_ortho_lowdin_overlap, (ao_num_align,ao_num)]
- BEGIN_DOC
+  implicit none
+  BEGIN_DOC
 ! overlap matrix of the ao_ortho_lowdin
 ! supposed to be the Identity
- END_DOC
- implicit none
- integer :: i,j,k,l
- double precision :: accu
- do i = 1, ao_num
-  do j = 1, ao_num
-   accu = 0.d0
-   do k = 1, ao_num
-    do l = 1, ao_num
-     accu = accu + ao_ortho_lowdin_coef(i,k) * ao_ortho_lowdin_coef(j,l) * ao_overlap(k,l)
+  END_DOC
+  integer                        :: i,j,k,l
+  double precision               :: c
+  do j=1, ao_num
+    do i=1, ao_num
+      ao_ortho_lowdin_overlap(i,j) = 0.d0
+    enddo
+  enddo
+  do k=1, ao_num
+    do j=1, ao_num
+      c = 0.d0
+      do l=1, ao_num
+        c = ao_ortho_lowdin_coef(j,l) * ao_overlap(k,l)
+      enddo
+      do i=1, ao_num
+        ao_ortho_lowdin_overlap(i,j) += ao_ortho_lowdin_coef(i,k) * c
+      enddo
     enddo
-   enddo
-   ao_ortho_lowdin_overlap(i,j) = accu
   enddo
- enddo
-
 END_PROVIDER