The charge-transfer band gap of the iron cyanide framework material Prussian Blue and its dependence on the type and location of the charge-compensating interstitial cations (K(+), Rb(+), Cs(+)) are investigated via periodic density functional (DF) calculations. The calculated variation in the band gap magnitude with respect to cation type confirms recent experimental results on cation-induced spectral shifts. The role of both the cation interaction with the framework and the cation-induced lattice expansion are examined with respect to their influence on the band gap. The gap magnitude is related to the cation type but is found to be more strongly affected by cation-induced lattice distortion as the cation passes through the material. Our results support the possibility of engineering the electronic structure of Prussian Blue type materials through guest-induced host-framework distortion.

We report the electronic and vibrational properties of Na 2 V 3 O 7 nanotubes and compare the response with other layered and nonlayered vanadates. The electronic structure of Na 2 V 3 O 7 displays a strong similarity to that of nontubular vanadates. We assign the 1.2-eV band as a V d f d excitation and the 3.3-and 3.9-eV bands as O 2p f V 3d charge-transfer structures. Although band structure calculations predict additional fine structure in the density of states because of the tubular morphology, such features are not observed in the absorption spectrum. The vibrational spectrum displays triplet mode splitting as a result of reduced site symmetry, consistent with the three sightly different vanadium atoms that form the basic structural unit. A low-frequency rattling mode is observed in Na 2 V 3 O 7 at 88 cm -1 . This unique characteristic of the Na + -ion intercalated tubes might be connected with the ionic conductivity.