We report the electronic structure and optical properties of the recently synthesized stable two-dimensional carbon allotrope-graphdiyne based on first-principles calculations and experimental optical spectrum. Due to the enhanced Coulomb interaction in reduced dimensionality, the band gap of graphdiyne increases to 1.10 eV within the GW many-body theory from a 0.44 eV within the density functional theory. The optical absorption is dominated by excitonic effects with remarkable electron-hole binding energy of over 0.55 eV within the GW-Bethe Salpeter equation calculation. Experimental optical absorption of graphdiyne films is performed and comparison with the theoretical calculations is analyzed in detail.

By using the density functional theory, we find that organometallic multidecker sandwich clusters V(2 n+1)Cp(2 n+2), Vn(FeCp2)(n+1) (Cp=cyclopentadienyl), and V(2n)Ant(n+1) (Ant=anthracene) may have linear structures, and their total magnetic moments generally increase with the cluster size. The one-dimensional (VCp)infinity, (VBzVCp)infinity (Bz=benzene), and (V2Ant)infinity wires are predicted to be ferromagnetic half-metals, while the one-dimensional (VCpFeCp)infinity wire is a ferromagnetic semiconductor. The spin transportation calculations show that the finite V2(n+1)Cp2(n+2) and Vn(FeCp2)(n+1) sandwich clusters coupled to gold electrodes are nearly perfect spin-filters.