  Accurate prediction of the electronic and hydrogen storage properties of
linear carbon chains (Cn) and Li-terminated linear carbon chains (Li2Cn), with
n carbon atoms (n = 5 - 10), has been very challenging for traditional
electronic structure methods, due to the presence of strong static correlation
effects. To meet the challenge, we study these properties using our newly
developed thermally-assisted-occupation density functional theory (TAO-DFT), a
very efficient electronic structure method for the study of large systems with
strong static correlation effects. Owing to the alteration of the reactivity of
Cn and Li2Cn with n, odd-even oscillations in their electronic properties are
found. In contrast to Cn, the binding energies of H2 molecules on Li2Cn are in
(or close to) the ideal binding energy range (about 20 to 40 kJ/mol per H2). In
addition, the H2 gravimetric storage capacities of Li2Cn are in the range of
10.7 to 17.9 wt%, satisfying the United States Department of Energy (USDOE)
ultimate target of 7.5 wt%. On the basis of our results, Li2Cn can be
high-capacity hydrogen storage materials for reversible hydrogen uptake and
release at near-ambient conditions.
