Theoretical investigation on the optical absorption spectra in cyclo[n]carbons (n=10, 14, 18)

The optical absorption spectra of cyclo[n]carbons (n=10, 14, 18) are investigated in the framework of time-dependent density functional theory. The collective plasmon excitations well develop as the increases of the ring size and the symmetry group of cyclo[n]carbons. An increase in intensity for the main peaks with the growing number of atoms in cyclo[n]carbons is observed. With the increase of the radius of the monocyclic ring, as more electrons participate in the dipole oscillation the main excitation peaks are red-shifted to the lower energy. The highly symmetrical structures of cyclo[n]carbons (D_{nh}) possess degenerate levels, leading to simpler spectra with fewer peaks. The Fourier transform of the induced electron density of the cyclo[n]carbons (n=10, 14, 18) is investigated at the excitation frequencies.