anchor.diff:  
               if (allowed_excitation) then
                   ! 3a. Probability of generating this excitation.
  -                pgen = calc_pgen_single_mol_no_renorm(connection%to_orb(1))
  +                pgen = pattempt_single*calc_pgen_single_mol_no_renorm(connection%to_orb(1))
   
                   ! 4a. Parity of permutation required to line up determinants.
                   call find_excitation_permutation1(cdet%f, connection)
  
positive.code: 
              if (allowed_excitation) then
                  ! 3a. Probability of generating this excitation.
                  pgen = calc_pgen_single_mol(cdet%occ_list, cdet%symunocc, connection%to_orb(1))
  
                  ! 4a. Parity of permutation required to line up determinants.
                  call find_excitation_permutation1(cdet%f, connection)
  
negative.code:         ! events.
  
          use basis, only: basis_fns
          use system, only: nel, nvirt, nvirt_alpha, nvirt_beta, sym0, sym_max
          use point_group_symmetry, only: nbasis_sym_spin, cross_product_pg_sym
  
  