Multiple GA runs were executed in parallel to explore a larger space, and the DFT results from all the GA runs were collected in a global database. This database was utilized not only to avoid redundant calculations but also to implement a migration operation, which was developed to mitigate premature convergence of GA by occasionally exchanging structures across different GA runs. A roulette method based on the above-derived fitness was employed to select the parent structures for the crossover and mutation operations as well as to implement the migration operation.