The Functionally-oriented Structure Design Of Graphene Quantum-dots

Graphene quantum-dots have the diversities of structures and properties which indicate a large potential application in the field of nano-devices.However,it is still a challenge to perform a systemic research about structures and properties of graphene quantum-dots due to the presence of numerous candidates.In this work,we showed an effective method that involved structural recognition,energy gap evaluation and Monte Carlo tree search.By using the structural recognition technology,we performed the first-principles high throughput calculations on structures with small carbon atoms.Considering the local bonding environment,we have determined six and thirteen types of inequivalent carbon atoms and carbon-carbon bonds,respectively.We proposed a tight-binding model with thirteen parameters fitted from the first-principles calculations data,which provided an ideal avenue to quickly evaluate the energy gaps of candidates with high accuracy.Combining the Monte Carlo tree search method and the congruence check,we determined the correlation between structures and the gap distributions as a function of carbon numbers,which is in agreement with the results from the first-principles calculations.The structural stabilities of the candidates with different numbers of hydrogen atoms might be modulated by the chemical potential of hydrogen,whereas the candidates with larger gaps might be more stable for the isomers with the same number of carbon and hydrogen atoms.Note that the energy gap of structures with high symmetries decrease with the size increasing,attributed to the quantum confinement effect.However,the maximum gaps we have found showed the property of fluctuation with increase in the number of carbon atoms,which reflects that the gap variation is dominated by the structural features.Our finding shows the gap variety of graphene quantum-dots due to the configuration diversity,which may extend the potential application of graphene quantum-dots in nano photo-electricity devices and fluorescence labeling in biomedicine.