The role of carbon impurities on the Si(0 0 1)-c(4 × 4) surface reconstruction: Theoretical calculations

In this work we employ the state-of-the-art pseudopotential method, within a generalized gradient approximation to the density functional theory, combined with a recently developed method for the calculation of HREELS spectra to study a series of different proposed models for carbon incorporation on the silicon (0 0 1) surface. A fully discussion on the geometry, energetics and specially the comparison between experimental and theoretical STM images and electron energy loss spectra indicate that the Si(1 0 0)-c(4 × 4) is probably induced by Si-C surface dimers, in agreement with recent experimental findings.     

Controllable Electronic Structures and Photoinduced Processes of Bay‐Linked Perylenediimide Dimers and a Ferrocene‐Linked Triad

A series of perylene‐3,4,9,10‐bis(dicarboximide) (PDI) dimers linked through the bay regions was systematically synthesized to examine the electronic structures and photophysical properties in dependence on the distance and orientation between the two PDI units. The spectroscopic and electrochemical measurements suggested that the coupling value of a directly linked PDI dimer (PDI)₂ is much larger than those of para‐ and meta‐phenylene‐bridged PDI dimers p‐(PDI)₂ and m‐(PDI)₂. The width of Davydov splitting was quantitatively evaluated to compare the coupling values between the two PDI units in these dimers by absorption spectroscopy in frozen 2‐methyl‐THF. Excimer formation of PDI dimers induced the strong fluorescence quenching and large red‐shifts. Femtosecond transient absorption revealed a broad absorption derived from an excimer in the range from about 600 nm to the near‐IR region. The rate constants of formation and decay of the excimer are strongly dependent on the coupling values. Time‐resolved measurements on ferrocene‐linked p‐(PDI)₂ revealed a competition between the photoinduced processes of electron transfer and excimer formation in PhCN, which is in sharp contrast with the sole electron‐transfer process in toluene.     

Transmission phase lapses at zero energy in graphene quantum dots

We address theoretically the electronic transport through graphene quantum dots with the emphasis on the transmission phase. Analytical and numerical results are presented regarding the existence – or not – of a π lapse of the transmittance phase (and, consequentially, a Fano zero in the transmittance) at the charge neutrality point. A simple universal criterium is found, the phase lapses being always present if the contact sites belong to the same sub‐lattice. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Reduced Graphene‐Wrapped MnO2 Nanowires Self‐Inserted with Co3O4 Nanocages: Remarkable Enhanced Performances for Lithium‐Ion Anode Applications

A simple synthetic approach for graphene‐templated nanostructured MnO₂ nanowires self‐inserted with Co₃O₄ nanocages is proposed in this work. The Co₃O₄ nanocages were penetrated in situ by MnO₂ nanowires. As an anode, the as‐obtained MnO₂–Co₃O₄–RGO composite exhibits remarkable enhanced performance compared with the MnO₂–RGO and Co₃O₄–RGO samples. The MnO₂–Co₃O₄–RGO electrode delivers a reversible capacity of up to 577.4 mA h g^?1 after 400 cycles at 500 mA g^?1 and the Coulombic efficiency of MnO₂–Co₃O₄–RGO is about 96 %.     

Structural and electronic properties of chiral single-wall copper nanotubes

The structural,energetic and electronic properties of chiral(n,m)(3≤n≤6,n/2≤m≤n)single-wall copper nanotubes(CuNTs)have been investigated by using projector-augmented wave method based on density-functional theory.The(4,3)CuNT is energetically stable and should be observed experimentally in both free-standing and tip-suspended conditions,whereas the(5,5)and(6,4)CuNTs should be observed in free-standing and tip-suspended conditions,respectively.The number of conductance channels in the CuNTs does not always correspond to the number of atomic strands comprising the nanotube.Charge density contours show that there is an enhanced interatomic interaction in CuNTs compared with Cu bulk.Current transporting states display different periods and chirality,the combined effects of which lead to weaker chiral currents on CuNTs.     

On the efficiency of VBSCF algorithms,a comment on “An efficient algorithm for energy gradients and orbital optimization in valence bond theory”

We comment on the paper [Song et al., J. Comput. Chem. 2009, 30, 399]. and discuss the efficiency of the orbital optimization and gradient evaluation in the Valence Bond Self Consistent Field (VBSCF) method. We note that Song et al. neglect to properly reference Broer et al., who published an algorithm [Broer and Nieuwpoort, Theor. Chim. Acta 1988, 73, 405] to use a Fock matrix to compute a matrix element between two different determinants, which can be used for an orbital optimization. Further, Song et al. publish a misleading comparison with our VBSCF algorithm [Dijkstra and van Lenthe, J. Chem. Phys. 2000, 113, 2100; van Lenthe et al., Mol. Phys. 1991, 73, 1159] to enable them to favorably compare their algorithm with ours. We give detail timings in terms of different orbital types in the calculation and actual timings for the example cases. © 2012 Wiley Periodicals, Inc.     

A weakly compressible MPS method for modeling of open‐boundary free‐surface flow

A mesh‐free particle method, based on the moving particle semi‐implicit (MPS) interaction model, has been developed for the simulation of two‐dimensional open‐boundary free‐surface flows. The incompressibility model in the original MPS has been replaced with a weakly incompressible model. The effect of this replacement on the efficiency and accuracy of the model has been investigated. The new inflow–outflow boundary conditions along with the particle recycling strategy proposed in this study extend the application of the model to open‐boundary problems. The final model is able to simulate open‐boundary free surface flow in cases of large deformation and fragmentation of free surface. The models and proposed algorithms have been validated and applied to sample problems. The results confirm the model's efficiency and accuracy. Copyright © 2009 John Wiley & Sons, Ltd.     

Electronic Structure and Thermoelectric Properties of Si-Based Clathrate Compounds

Thermoelectric properties of Au-substituted Si-based clathrates, Ba₈AuGa₁₃Si₃₂ and Ba₆A₂AuGa _x Si_45−x (A = Sr, Eu, x = 13, 14), were experimentally and theoretically investigated. The polycrystalline samples of the Au-substituted Si-based clathrates were prepared by using the spark plasma sintering technique. The electronic structure of Ba₆A₂AuGa₁₃Si₃₂ was theoretically calculated by ab initio calculations, and the thermoelectric properties of Ba₆A₂AuGa _x Si_45−x were estimated through the calculated electronic structure. The effective mass of Ba₆A₂AuGa _x Si_45−x was experimentally estimated to be greater than that of Ba₈AuGa₁₃Si₃₂. Experimentally observed electronic properties agree with the calculations for Ba₆A₂AuGa _x Si_45−x . The maximum ZT value of Ba₆Sr₂AuGa₁₄Ge₃₁ is about 0.5 at 850 K. The calculated thermoelectric properties agree very well with the experimental results in the range from room temperature to 900 K.     

Spectrally‐Efficient Decode‐and‐Forward Scheme Based on Constellation Rotation

A spectrally‐efficient scheme is proposed for orthogonal decode‐and‐forward relaying. By utilizing constellation rotation, the scheme can achieve twice the spectral efficiency as that of the conventional one, with low implementation complexity. It can offer a full diversity order as well, whereas the loss in coding gain is less than 1 dB for practical environments.