Bonding and magnetism in nanosized graphene molecules: Singlet states of zigzag edged hexangulenes C_{6 m}² H_6m (m=2,3,⋯,10)

A novel molecular phenomenon is predicted on the basis of trends identified in an ab initio density functional theory study of the electronic and geometric structure of the hexagonal shaped zigzag edged graphene hydrocarbon molecules C_{6 m}² H_6m (m=2,⋯,10). Electrons in the interior organize to form a graphene core that grows with edge size m. Electrons in the highest occupied molecular orbital levels, localized primarily on the perimeter carbons, polarize the interior atoms with a intensity that decays rapidly with distance from the perimeter. Three distinctive bond length patterns emerge: (i) a central graphene core that grows with size m; (ii) shape-similar transverse and radial bond length patterns on interior rows close to the edges; and (iii) quinoidal bonds radiating from each apex that link adjacent edges. Concomitant with these changes are: (i) a monotonic decrease in atomic charge from center to perimeter and (ii) relegation of spin in diradical states to the outer atomic rows of the bipartite lattice.