anchor.diff:  
               ! Update the energy estimators (shift & projected energy).
               call update_energy_estimators(nparticles_old)
  +            ! TEMPORARY: population on reference determinant.
  +            ! As we might select the reference determinant multiple times in
  +            ! a cycle, the running total of D0_population is incorrect (by
  +            ! a factor of the number of times it was selected).  Fix.
  +            call search_walker_list(f0, 1, tot_walkers, hit, pos)
  +            D0_population = walker_population(1,pos)
   
               call cpu_time(t2)
   
  
positive.code:             ! Must be the reference.
              cdet%f = f0
              excitation_level = 0
              amplitude = D0_population ! TODO: don't accumulate D0 over report loops
              ! Only one cluster of this size to choose => p_clust = 1
          case default
              ! Select cluster from the excitors on the current processor in
  
negative.code:             ! Zero report cycle quantities.
              proj_energy = 0.0_p
              rspawn = 0.0_p
              ! TEMPORARY
              D0_normalisation = nint(D0_population)
              D0_population = 0.0_p
  
              do icycle = 1, ncycles
  