diff --git a/src/csf/sigma_vector.irp.f b/src/csf/sigma_vector.irp.f
index 0f3f093c..581a6a6b 100644
--- a/src/csf/sigma_vector.irp.f
+++ b/src/csf/sigma_vector.irp.f
@@ -4,58 +4,47 @@
 &BEGIN_PROVIDER [ integer, NBFMax]
 &BEGIN_PROVIDER [ integer, n_CSF]
 &BEGIN_PROVIDER [ integer, maxDetDimPerBF]
-   implicit none
-
-   BEGIN_DOC
- ! The maximum number of SOMOs for the current calculation.
- ! required for the calculation of prototype arrays.
-   END_DOC
-
-   integer                        :: i,j,k,l
-   integer                        :: startdet,enddet
-   integer                        :: ncfg,ncfgprev
-   integer                        :: NSOMO
-   integer                        :: dimcsfpercfg
-   integer                        :: detDimperBF
-   real*8                         :: coeff
-   integer                        :: MS
-   integer                        :: ncfgpersomo
-   double precision               :: bin_1, bin_2
-
-   NSOMOMax = min(elec_num, cfg_nsomo_max + 2)
-
-   bin_1 = binom(NSOMOMax, (NSOMOMax+1)/2)
-   bin_2 = binom(NSOMOMax,((NSOMOMax+1)/2)+1)
-
-   ! Note that here we need NSOMOMax + 2 sizes
-   NCSFMax = max(1,int(bin_1-bin_2))
-   NBFMax = NCSFMax
-   maxDetDimPerBF = max(1,nint((binom(NSOMOMax,(NSOMOMax+1)/2))))
-   NMO = n_act_orb
-
-   detDimperBF = 0
-   MS = elec_alpha_num-elec_beta_num
-
-   ! number of cfgs = number of dets for 0 somos
-   n_CSF = cfg_seniority_index(0)-1
-   ncfgprev = cfg_seniority_index(0)
-   do i = 0-iand(MS,1)+2, cfg_nsomo_max,2
-     if(cfg_seniority_index(i) == -1)then
-       ncfgpersomo = N_configuration + 1
-     else
-       ncfgpersomo = cfg_seniority_index(i)
-     endif
-     ncfg = ncfgpersomo - ncfgprev
-     if (i > 2) then
-       bin_1 = binom(i-2, (i-2+1)/2)
-       bin_2 = binom(i-2,((i-2+1)/2)+1)
-       dimcsfpercfg = max(1,int(bin_1-bin_2))
-     else
-       dimcsfpercfg = 1
-     endif
-     n_CSF += ncfg * dimcsfpercfg
-     ncfgprev = cfg_seniority_index(i)
-   enddo
+  implicit none
+  BEGIN_DOC
+  ! Documentation for NSOMOMax
+  ! The maximum number of SOMOs for the current calculation.
+  ! required for the calculation of prototype arrays.
+  END_DOC
+  NSOMOMax = min(elec_num, cfg_nsomo_max + 2)
+  ! Note that here we need NSOMOMax + 2 sizes
+  NCSFMax = max(1,nint((binom(NSOMOMax,(NSOMOMax+1)/2)-binom(NSOMOMax,((NSOMOMax+1)/2)+1)))) ! TODO: NCSFs for MS=0
+  NBFMax = NCSFMax
+  maxDetDimPerBF = max(1,nint((binom(NSOMOMax,(NSOMOMax+1)/2))))
+  NMO = n_act_orb
+  integer i,j,k,l
+  integer startdet,enddet
+  integer ncfg,ncfgprev
+  integer NSOMO
+  integer dimcsfpercfg
+  integer detDimperBF
+  real*8 :: coeff
+  integer MS
+  integer ncfgpersomo
+  detDimperBF = 0
+  MS = elec_alpha_num-elec_beta_num
+  ! number of cfgs = number of dets for 0 somos
+  n_CSF = 0
+  ncfgprev = cfg_seniority_index(0)
+  do i = iand(MS,1), NSOMOMax-2,2
+    if(cfg_seniority_index(i+2) .EQ. -1) then
+      ncfgpersomo = N_configuration + 1
+    else
+      ncfgpersomo = cfg_seniority_index(i+2)
+    endif
+    ncfg = ncfgpersomo - ncfgprev
+    if(iand(MS,1) .EQ. 0) then
+      dimcsfpercfg = max(1,nint((binom(i,i/2)-binom(i,i/2+1))))
+    else
+      dimcsfpercfg = max(1,nint((binom(i,(i+1)/2)-binom(i,(i+3)/2))))
+    endif
+    n_CSF += ncfg * dimcsfpercfg
+    ncfgprev = cfg_seniority_index(i+2)
+  enddo
 END_PROVIDER