anchor.diff:                  hmatel = get_one_body_int_mol(one_e_ints, one_e_ints_im, i, a, sys)
   
                   do iel = 1, sys%nel
  -                    if (occ_list(iel) /= i) &
  +                    if (occ_list(iel) /= i) then
                           hmatel = hmatel &
                               + get_two_body_int_mol(coulomb_ints, coulomb_ints_im, i, occ_list(iel), a, occ_list(iel), &
  -                                                    sys) &
  -                            - get_two_body_int_mol(coulomb_ints, coulomb_ints_im, i, occ_list(iel), occ_list(iel), a, &
                                                       sys)
  +                        if (sys%read_in%extra_exchange_integrals) then
  +                            hmatel = hmatel &
  +                                        - get_two_body_exchange_pbc_int_complex(sys%read_in%additional_exchange_ints, &
  +                                        sys%read_in%additional_exchange_ints_imag, i, occ_list(iel), occ_list(iel), a, sys)
  +
  +                        else
  +                            hmatel = hmatel &
  +                                - get_two_body_int_mol(coulomb_ints, coulomb_ints_im, i, occ_list(iel), occ_list(iel), a, &
  +                                                    sys)
  +                        end if
  +                    end if
                   end do
               end associate
   
  
positive.code:         ! symmetry).  This is less safe that slater_condon1_mol but much faster
          ! as it allows symmetry checking to be skipped in the integral lookups.
  
          use molecular_integrals, only: get_one_body_int_mol_nonzero, get_two_body_int_mol_nonzero
          use system, only: sys_t
          use hamiltonian_data, only: hmatel_t
  
  
negative.code:         !    <D|H|D>, the diagonal Hamiltonian matrix element involving D for
          !    systems defined by integrals read in from an FCIDUMP file.
  
          use molecular_integrals, only: get_one_body_int_mol_nonzero, get_two_body_int_mol_nonzero, &
                                          get_two_body_exchange_pbc_int_nonzero
          use system, only: sys_t
  
          complex(p) :: hmatel
  