diff --git a/make.config.gfortran b/make.config.gfortran
index ac6352b..6e5b0e6 100644
--- a/make.config.gfortran
+++ b/make.config.gfortran
@@ -7,7 +7,7 @@ CPU_TYPE="-mavx"
 ## FORTRAN compiler
 FC="gfortran -ffree-line-length-none"
 FCFLAGS="-O2 -g ${CPU_TYPE}"
-LIB="-lblas -llapack -lpthread"
+LIB="-lblas -llapack -lpthread -lqmckl"
 
 ## IRPF90
 IRPF90="${QMCCHEM_PATH}/bin/irpf90"
diff --git a/src/det.irp.f b/src/det.irp.f
index 71488b2..6218438 100644
--- a/src/det.irp.f
+++ b/src/det.irp.f
@@ -20,7 +20,8 @@ END_PROVIDER
 
 END_PROVIDER
 
-subroutine det_update(n,LDS,m,l,S,S_inv,d)
+ subroutine det_update(n,LDS,m,l,S,S_inv,d)
+  use qmckl
   implicit none
 
   integer, intent(in)            :: n,LDS  ! Dimension of the vector
@@ -30,169 +31,245 @@ subroutine det_update(n,LDS,m,l,S,S_inv,d)
   real,intent(inout)             :: S(LDS,n)     ! Slater matrix
   double precision,intent(inout) :: S_inv(LDS,n) ! Inverse Slater matrix
   double precision,intent(inout) :: d            ! Det(S)
+  double precision               :: zl, lambda, d_inv
 
   if (d == 0.d0) then
     return
   endif
-  select case (n)
-      case default
-      call det_update_general(n,LDS,m,l,S,S_inv,d)
-    BEGIN_TEMPLATE
-      case ($n)
-        call det_update$n(n,LDS,m,l,S,S_inv,d)
-    SUBST [n]
-    1;;
-    2;;
-    3;;
-    4;;
-    5;;
-    6;;
-    7;;
-    8;;
-    9;;
-    10;;
-    11;;
-    12;;
-    13;;
-    14;;
-    15;;
-    16;;
-    17;;
-    18;;
-    19;;
-    20;;
-    21;;
-    22;;
-    23;;
-    24;;
-    25;;
-    26;;
-    27;;
-    28;;
-    29;;
-    30;;
-    31;;
-    32;;
-    33;;
-    34;;
-    35;;
-    36;;
-    37;;
-    38;;
-    39;;
-    40;;
-    41;;
-    42;;
-    43;;
-    44;;
-    45;;
-    46;;
-    47;;
-    48;;
-    49;;
-    50;;
-    51;;
-    52;;
-    53;;
-    54;;
-    55;;
-    56;;
-    57;;
-    58;;
-    59;;
-    60;;
-    61;;
-    62;;
-    63;;
-    64;;
-    65;;
-    66;;
-    67;;
-    68;;
-    69;;
-    70;;
-    71;;
-    72;;
-    73;;
-    74;;
-    75;;
-    76;;
-    77;;
-    78;;
-    79;;
-    80;;
-    81;;
-    82;;
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-    84;;
-    85;;
-    86;;
-    87;;
-    88;;
-    89;;
-    90;;
-    91;;
-    92;;
-    93;;
-    94;;
-    95;;
-    96;;
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-    99;;
-    100;;
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-    102;;
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-    104;;
-    105;;
-    106;;
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-    108;;
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-    110;;
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-    136;;
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-    140;;
-    141;;
-    142;;
-    143;;
-    144;;
-    145;;
-    146;;
-    147;;
-    148;;
-    149;;
-    150;;
-    END_TEMPLATE
-  end select
+
+!! -- START QMCKL/SMW ADDITIONS -- !!
+!!                                 !!
+  integer :: i, j
+  integer (qmckl_exit_code) :: rc
+  integer (qmckl_context) :: context
+  integer(kind=8) :: ddim, nupdates, updates_index(1)
+  real(c_double) :: updates(n,1), breakdown
+  double precision :: S_inv_sq(n,n)
+
+  S_inv = S_inv / d
+
+  ! open(unit = 2000, file = "Slater_old.dat")
+  ! open(unit = 3000, file = "Slater_old_inv.dat")
+  ! do i=1,n
+  !   do j=1,n
+  !     write(2000,"(E23.15, 1X)", advance="no") S(j,i) ! write transpose for Octave
+  !     write(3000,"(E23.15, 1X)", advance="no") S_inv(i,j)
+  !   end do
+  !   write(2000,*)
+  !   write(3000,*)
+  ! end do
+  ! flush(2000)
+  ! flush(3000)
+  ! close(2000)
+  ! close(3000)
+
+  do i=1,n
+    updates(i,1) = m(i) - S(i,l) ! transform repl. upds. into additive upds.
+    S(i,l) = m(i) ! update S with repl. upds
+  end do
+
+  zl = 0
+  do i=1,n
+    zl = zl + S_inv(i,l) * updates(i,1)
+  end do
+
+  d_inv = 1.d0/d
+  d = d + zl
+  lambda = d * d_inv
+  if ( dabs(lambda) < 1.d-3 ) then
+    d = 0.d0
+    return
+  endif
+
+  context = qmckl_context_create()
+  ddim = n
+  nupdates = 1
+  updates_index(1) = l
+  breakdown = 1e-3
+  S_inv_sq = S_inv(1:n,1:n)
+  rc = qmckl_sherman_morrison_splitting(context, ddim, nupdates, updates, updates_index, breakdown, S_inv_sq)
+  S_inv = S_inv_sq(1:n,1:n)
+  rc = qmckl_context_destroy(context)
+
+  ! open(unit = 4000, file = "Slater.dat")
+  ! open(unit = 5000, file = "Slater_inv.dat")
+  ! do i=1,n
+  !   do j=1,n
+  !     write(4000,"(E23.15, 1X)", advance="no") S(j,i) ! write transpose for Octave
+  !     write(5000,"(E23.15, 1X)", advance="no") S_inv(i,j)
+  !   end do
+  !   write(4000,*)
+  !   write(5000,*)
+  ! end do
+  ! flush(4000)
+  ! flush(5000)
+  ! close(4000)
+  ! close(5000)
+
+  S_inv = S_inv * d
+
+  ! select case (n)
+  !     case default
+  !     call det_update_general(n,LDS,m,l,S,S_inv,d)
+  !   BEGIN_TEMPLATE
+  !     case ($n)
+  !       call det_update$n(n,LDS,m,l,S,S_inv,d)
+  !   SUBST [n]
+  !   1;;
+  !   2;;
+  !   3;;
+  !   4;;
+  !   5;;
+  !   6;;
+  !   7;;
+  !   8;;
+  !   9;;
+  !   10;;
+  !   11;;
+  !   12;;
+  !   13;;
+  !   14;;
+  !   15;;
+  !   16;;
+  !   17;;
+  !   18;;
+  !   19;;
+  !   20;;
+  !   21;;
+  !   22;;
+  !   23;;
+  !   24;;
+  !   25;;
+  !   26;;
+  !   27;;
+  !   28;;
+  !   29;;
+  !   30;;
+  !   31;;
+  !   32;;
+  !   33;;
+  !   34;;
+  !   35;;
+  !   36;;
+  !   37;;
+  !   38;;
+  !   39;;
+  !   40;;
+  !   41;;
+  !   42;;
+  !   43;;
+  !   44;;
+  !   45;;
+  !   46;;
+  !   47;;
+  !   48;;
+  !   49;;
+  !   50;;
+  !   51;;
+  !   52;;
+  !   53;;
+  !   54;;
+  !   55;;
+  !   56;;
+  !   57;;
+  !   58;;
+  !   59;;
+  !   60;;
+  !   61;;
+  !   62;;
+  !   63;;
+  !   64;;
+  !   65;;
+  !   66;;
+  !   67;;
+  !   68;;
+  !   69;;
+  !   70;;
+  !   71;;
+  !   72;;
+  !   73;;
+  !   74;;
+  !   75;;
+  !   76;;
+  !   77;;
+  !   78;;
+  !   79;;
+  !   80;;
+  !   81;;
+  !   82;;
+  !   83;;
+  !   84;;
+  !   85;;
+  !   86;;
+  !   87;;
+  !   88;;
+  !   89;;
+  !   90;;
+  !   91;;
+  !   92;;
+  !   93;;
+  !   94;;
+  !   95;;
+  !   96;;
+  !   97;;
+  !   98;;
+  !   99;;
+  !   100;;
+  !   101;;
+  !   102;;
+  !   103;;
+  !   104;;
+  !   105;;
+  !   106;;
+  !   107;;
+  !   108;;
+  !   109;;
+  !   110;;
+  !   111;;
+  !   112;;
+  !   113;;
+  !   114;;
+  !   115;;
+  !   116;;
+  !   117;;
+  !   118;;
+  !   119;;
+  !   120;;
+  !   121;;
+  !   122;;
+  !   123;;
+  !   124;;
+  !   125;;
+  !   126;;
+  !   127;;
+  !   128;;
+  !   129;;
+  !   130;;
+  !   131;;
+  !   132;;
+  !   133;;
+  !   134;;
+  !   135;;
+  !   136;;
+  !   137;;
+  !   138;;
+  !   139;;
+  !   140;;
+  !   141;;
+  !   142;;
+  !   143;;
+  !   144;;
+  !   145;;
+  !   146;;
+  !   147;;
+  !   148;;
+  !   149;;
+  !   150;;
+  !   END_TEMPLATE
+  ! end select
+
+!!                               !!
+!! -- END QMCKL/SMW ADDITIONS -- !!
 end
 
 subroutine det_update2(n,LDS,m,l,S,S_inv,d)
@@ -430,7 +507,7 @@ SUBST [ n ]
 
 END_TEMPLATE
 
-BEGIN_TEMPLATE
+BEGIN_TEMPLATE  
 ! Version for mod(n,4) = 1
 subroutine det_update$n(n,LDS,m,l,S,S_inv,d)
   implicit none
@@ -1186,7 +1263,7 @@ END_PROVIDER
   BEGIN_DOC
   ! det_alpha_value_curr : Value of the current alpha determinant
   !
-  ! det_alpha_value_curr : Slater matrix for the current alpha determinant.
+  ! slater_matrix_alpha : Slater matrix for the current alpha determinant.
   !  1st index runs over electrons and
   !  2nd index runs over MOs.
   !  Built with 1st determinant
@@ -1200,6 +1277,7 @@ END_PROVIDER
   double precision               :: tmp_inv(elec_alpha_num_8)
   real                           :: tmp_det(elec_alpha_num_8)
   integer, save                  :: ifirst
+  logical                        :: file_exists
   !DIR$ ATTRIBUTES ALIGN : $IRP_ALIGN :: tmp_inv, tmp_det
 
   if (ifirst == 0) then
@@ -1211,12 +1289,12 @@ END_PROVIDER
   endif
 
   PROVIDE mo_value
-  if (det_i /= det_alpha_order(1) ) then
+  if (det_i /= det_alpha_order(1) ) then ! alpha determinant order changes
 
     n_to_do = 0
     do k=1,elec_alpha_num
       imo = mo_list_alpha_curr(k)
-      if ( imo /= mo_list_alpha_prev(k) ) then
+      if ( imo /= mo_list_alpha_prev(k) ) then ! mo for electron k has changed
           n_to_do += 1
           to_do(n_to_do) = k
       endif
@@ -1288,14 +1366,14 @@ END_PROVIDER
     ddet = 0.d0
 
     if (n_to_do < shiftl(elec_alpha_num,1)) then
-
       do while ( n_to_do > 0 )
-        ddet = det_alpha_value_curr
-        n_to_do_old = n_to_do
+        ddet = det_alpha_value_curr ! remember value of det_alpha_value_curr
+        n_to_do_old = n_to_do ! remember n_to_do value
         n_to_do = 0
         do l=1,n_to_do_old
-          k = to_do(l)
-          imo = mo_list_alpha_curr(k)
+          k = to_do(l) ! select electron to change
+          imo = mo_list_alpha_curr(k) ! select mo to change
+          ! write(*,*) "k, imo, mo_value(1,imo) = ", k, imo, mo_value(1,imo)
           call det_update(elec_alpha_num, elec_alpha_num_8,            &
               mo_value(1,imo),                                         &
               k,                                                       &
@@ -1344,12 +1422,13 @@ END_PROVIDER
         slater_matrix_alpha_inv_det(k,i) = mo_value(i,mo_list_alpha_curr(k))
       enddo
     enddo
+    ! write(*,*) "FIRST TIME OR ALL FAILED; DO LAPACK"
     call invert(slater_matrix_alpha_inv_det,elec_alpha_num_8,elec_alpha_num,ddet)
-
   endif
   ASSERT (ddet /= 0.d0)
 
   det_alpha_value_curr = ddet
+
 END_PROVIDER
 
  BEGIN_PROVIDER [ double precision, det_beta_value_curr ]
@@ -1467,6 +1546,7 @@ END_PROVIDER
         ddet = det_beta_value_curr
         n_to_do_old = n_to_do
         n_to_do = 0
+        loopcount = 0
         do l=1,n_to_do_old
           k = to_do(l)
           imo = mo_list_beta_curr(k)
diff --git a/src/qmckl b/src/qmckl
index de03986..8535e3c 160000
--- a/src/qmckl
+++ b/src/qmckl
@@ -1 +1 @@
-Subproject commit de03986bda2be207377875ed5a0852cb721b86b9
+Subproject commit 8535e3c0b5a4f4194ca0400b348774c3cc7c74d0