docs: def site_specific_nn_occupation( self ):
          """
          Returns the number of occupied nearest neighbour sites, classified by site type.
  
          Args:
              None
  
          Returns:
              (Dict(Str:Int)): Dictionary of nearest-neighbour occupied site numbers, classified by site label, e.g. { 'A' : 2, 'B' : 1 }.
          """
          to_return = { l : 0 for l in set( ( site.label for site in self.p_neighbours ) ) }
          for site in self.p_neighbours:
              if site.is_occupied:
               to_return[ site.label ] += 1
          return to_return