We set up an evolutionary algorithm combined with density functionaltight-binding (DFTB) calculations to investigate hydrogen adsorption on flatgraphene and graphene monolayers curved over substrate steps. During theevolution, candidates for the new generations are created by adsorption of anadditional hydrogen atom to the stable configurations of the previousgeneration, where a mutation mechanism is also incorporated. Afterwards atwo-stage selection procedure is employed. Selected candidates act as theparents of the next generation. In curved graphene, the evolution follows asimilar path except for a new mechanism, which aligns hydrogen atoms on theline of minimum curvature. The mechanism is due to the increased chemicalreactivity of graphene along the minimum radius of curvature line (MRCL) and to sp3 bond angles being commensurate with the kinked geometry of hydrogenatedgraphene at the substrate edge. As a result, the reaction barrier is reducedconsiderably along the MRCL, and hydrogenation continues like a mechanicalchain reaction. This growth mechanism enables lines of hydrogen atoms along theMRCL, which has the potential to overcome substrate or rippling effects andcould make it possible to define edges or nanoribbons without actually cuttingthe material.
Özbal, G., Falkenberg, J. T., Brandbyge, M., Senger, R. T., & Sevincli, H. (2018). Directed growth of hydrogen lines on graphene: High-throughput simulations powered by evolutionary algorithm. Physical Review Materials, 2(7), . https://doi.org/10.1103/PhysRevMaterials.2.073406