First-principles modeling of the polycyclic aromatic hydrocarbons   reduction
  Density functional theory modelling of the reduction of realistic nanographene molecules (C42H18, C48H18 and C60H24) by molecular hydrogen evidences for the presence of limits in the hydrogenation process. These limits caused the contentions between three-fold symmetry of polycyclic aromatic hydrocarbon molecules and two-fold symmetry of adsorbed hydrogen pairs. Increase of the binding energy between nanographenes during reduction is also discussed as possible cause of the experimentally observed limited hydrogenation of studied nanographenes. 
D. W. Boukhvalov, X. Feng, K. M\"ullen
cond-mat.mtrl-sci cond-mat.mes-hall