The worst scoring molecule has a normalized score of 0 and the rest a number between 0 and 1, with all scores summing to 1. Molecules are then selected for mating and mutation using roulette selection and these normalized scores. We found that occasionally the bonding in the ligands rearranged and these were discarded by giving them an artificially high energy score of 9999, ensuring removal from the population. The connectivity is computed based on the overlap charge density from an extended Hückel calculation.