Carbon Material with a Highly Ordered Linear-Chain Structure - Polyynes: Synthesis, Properties, and Applications - page 220

FIGURE 11.6 Calculated DOVS of cumulene chain without kinks (a) and with
periodical kinks (55 ), dotted symbol experiment.

marked by the gray color below the Fermi level. The experimental curves of
DOVS are shown in the same figure by the pointed line. As can be seen from
the figure, the calculated position of the

-bond sub-band lies at exactly the
same position as the experimental DOVS in the region of 19 eV to 27 eV.
The calculated low energy edge of the p -band at 16 eV lies also at a similar

energy value as that obtained experimentally. The

* anti-bonding band is
found to be empty. The cumulene chain should be a metal as the Fermi level
E f falls into the p -band. The maximum on the experimental curve at 12 eV
is located close to the calculate Fermi level but does not fit well with the
calculated DOVS. The presence of this peak can be explained by the
appearance of the forbidden gap due to metal-dielectric transition, which is
a characteristic property of one-dimensional systems with the half-filled
valence band. This result is in good agreement with the theory of one-
dimensional transition in carbon chains (Peierls transition or dimerization
[12], charge density and spin density waves without dimerization [13,14]).
According to these theories, carbon chains with equally spaced carbon