Quantum chemical studies of carbon-based graphene-like nanostructures: from benzene to coronene.

Context: This study presents quantum chemical analysis of 14 distinct carbon-based nanostructures (CBN), ranging from simple molecules, like benzene, to more complex structures, such as coronene, which serves as an exemplary graphene-like model. The investigation focuses on elucidating the relationships between molecular orbital (MO) energies, the energy band gaps, electron occupation numbers (eON), electronic conduction, and the compound topologies, seeking to find the one that approaches most of a graphene-like structure for in silico studies. Through detailed examination of molecular properties including chemical hardness and chemical potential, we demonstrate that the electronic exchange between orbitals is directly influenced by the structural topology of the carbon-based nanostructures, as the electron occupation numbers and the molecular orbital energies. Raman theoretical analysis was performed, ensuring the approximation to a graphene structure by its experimental fingerprint comparison. The correlations presented here offer an approach for anticipating electronic conductivity in graphene-like materials, as well as the confirmation of coronene as a graphene nanostructure for theoretical analyses.

Method: The models were designed at Ghemical software optimized at Tripos5.2 force field and properly protonated on the peripheral carbons. The models were then optimized by PM7 semiempirical method using MOPAC2016 to minimize the gradient energy before applying the DFT calculations. After that, the model's geometry was finally optimized at ab initio B3LYP hybrid functional and 6-31 G* basis, using ORCA5.0.4. The eON, the MO energies and the Raman spectrum were obtained with the same methods, making possible the spectrum extraction without the interference of H atoms, approaching the analyses to graphene-like topologies.