Quantum chemical modeling of infrared and Raman activities in lithium-doped amorphous carbon nanostructures:: hexa-peri-hexabenzocoron as a model for hydrogen-rich carbon materials

The preferential sites for lithium doping in hydrogen-rich amorphous carbon materials are investigated by considering, as a model, a large polycyclic aromatic hydrocarbon (PAH): hexa-peri-hexabenzocoronene. Quantum-chemical calculations are carried out with B3LYP/6-31G* density functional theory to study the lowest energy configurations of the PAH doped with two lithium atoms. Infrared and Raman activities are computed for the most stable configurations and compared with the spectra of the pristine material to disclose the effect of doping on the vibrational spectra of hydrogen-rich amorphous carbon materials. It is shown that interaction with lithium atoms perturbs appreciably the atomic and electronic structure of the nanometric graphene sheet and leads to new marker bands in the spectra. (C) 2003 Elsevier Ltd. All rights reserved.