Evolution of the plasmon spectrum of C28Hn with the passivation of dangling bonds

The evolution of the π-plasmon spectrum of C28Hn (0 ⩽ n ⩽ 28), calculated in time dependent local density approximation making use of norm-conserving pseudopotentials, testifies to the fact that the passivation of the dangling bonds of C28 leads to systems which are progressively more polarizable, as expected for closed shell systems with the increasing number of electrons, with the exception of the system C28H28 which displays a conspicuous departure from this behaviour. This phenomenon is understood in terms of a reduction of the spill-out of the π-electrons from the surface of the system.