Probing the structural, electronic and optical properties of pure and B, N, or Li substituted Cyclo-18 ring: density functional theory investigations

Employing the quantum computational approach by using the Density Functional Theory along with GGA exchange correlation functional, we have investigated the structural, electronic, and optical properties of Cyclo-18 ring containing 18 sp hybridized carbon atoms and substituted Cyclo-C17X (X = B, N, and Li) ring. The Cyclo-18 ring has two opposite pi electron system that can be organized as a D9h polyynic and D18h cumulene form. Our computational simulations suggest that D9h polyynic structure is minimum energy structure. Alkali metal doping makes C18 metallic by lowering the band gap when compared to the pure C18 (5.02eV). The strength of the chemical bonding analyzed using average binding energies for the Li, B, and N substituted Cyclo-C18 ring which are -4.58 eV, -4.65 eV, and -2.83 eV respectively. The positive charges on B, N and Li and negative charges on the Cyclo-18 ring demonstrate the partial Coulomb interactions and also charge transfer from B, N, and Li to Cyclo-18 ring. It is also found that the dominant adsorption IR peak at 2049 cm-1, 1329 cm-1, and 1011 cm-1 for B, N, and Li substituted C18 ring. There is an enhancement in optical absorption in the visible region due to doping which makes the system suitable for photo-catalytic applications.