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[en] We present first-principles calculations of the structural and electronic properties of liquid nitrogen in the pressure-temperature range of 0-200 GPa and 2000-6000 K. The molecular-polymerization and molecular-atomic liquid phase boundaries have been mapped over this region. We find the polymeric liquid to be metallic, similar to what has been reported for the higher-temperature atomic fluid. An explanation of the electronic properties is given based on the structure and bonding character of the transformed liquids. We discuss the structural and bonding differences between the polymeric liquid and insulating solid cubic-gauche nitrogen to explain the differences in their electronic properties. Furthermore, we discuss the mechanism responsible for charge transport in polymeric nitrogen systems to explain the conductivity of the polymeric fluid and the semi-conducting nature of low-temperature amorphous nitrogen.
[en] Complete text of publication follows. Migration of excess charges through DNA has been a focus of considerable interest. So far most theoretical works were restricted to the description of charge motion along the well-defined static DNA structure. The two important parameters that determine the mechanism of charge transfer in DNA are site energies and charge transfer integrals. Both parameters critically depend on geometric fluctuations in DNA. I describe the magnitude of fluctuations in energies and charge transfer integrals along the donor-DNA-acceptor system. The consequences of fluctuations are discussed using stilbene-capped DNA hairpins. We exploited molecular dynamics simulations and density functional theory calculations to study the time-scale of fluctuations in the site energies and charge transfer integrals. The results were used in tight-binding calculations to evaluate the effects of structural fluctuations on hole transfer in the DNA hairpins. The injection energy barrier is higher than the average values of the charge transfer integrals. The fluctuations in site energies and charge transfer integrals are sufficiently large to lead to the domination of a fluctuation-assisted incoherent transport. The difference between the present and previous explanations is the lack of a priori assumptions about a change in the transport mechanism (from superexchange to hopping) typical for earlier works. In contrast with earlier studies, the proposed model of charge transport in fluctuating (rather than static) DNA structure provides a theoretical framework to describe the process for all bridge lengths. The results are in agreement with the full range of experimental data.
[en] We investigate the apparent charge transfer between adatoms in the GeXPb[l.XjGe(lll) interface both experimentally and theoretically. Scanning tunneling microscopy and surface core level measurements suggest significant charge transfer from the Ge adatoms to the Pb adatoms. However, first-principles calculations unambiguously find that the total electronic displacement is negligibly small, and that the results of published experiments can be explained as a result of bond rearrangement
[en] Complete text of publication follows. The solvent dependent dual fluorescence of 4-dimethylaminobenzonitrile (DMABN) originated from a locally excited state (LE) and twisted intramolecular charge transfer (TICT) state that is stabilized in polar solvents. It has been the subject of intense experimental and theoretical work since its discovery in 1959. It can be expected that DMABN can form a halogen-bonding complex with a halogen atom as Fig. 1. Herein the fluorescence of DMABN alone and with carbon tetrabromide (CBr4) or diiodoperfluorohexane was investigated in different solvents. Upon addition of CBr4 or diiodoperfluorohexane, both LE and TICT peak decreased, but TICT peak decreased more sharply, as showed in Fig. 2. The halogen-bonding may disturb the TICT state by CT between Br and N atom. Also Br quenches dual fluorescence by heavy atom effect. So fluorescence from TICT state decreased more quickly than that from LE state.
[en] Current-induced forces can excite molecules, polymers and other low-dimensional materials, which in turn leads to an effective gate voltage through Holstein interaction. Here, by taking a short asymmetric DNA junction as an example, and using the Langevin approach, we find that when suppression of charge transport by the effective gate voltage surpasses the current increase from an elevated voltage bias, the current-voltage (I–V) curves display strong negative differential resistance (NDR) and perfect current-switching characteristics. The asymmetric DNA chain differs in mechanical stability under inverse voltages and the I–V curve is asymmetric about inverse biases, which can be used to understand recent transport experiments on DNA chains, and meanwhile provides a new strategy to realize NDR in molecular junctions and other low-dimensional quantum systems. (paper)
[en] We investigate charge transport behaviour in colloidal ZnO nanocrystal solids with different surface states. Our results show that the logarithm of the conductivity scales with −T−1/4, suggestive of Mott variable-range hopping. Analysis of the density of states at the Femi level suggests that the charge hopping occurs through surface or defect states, rather than by direct hopping between quantum-confined conduction band states of the nanocrystals
[en] This article has been retracted: please see Elsevier Policy on Article Withdrawal ( (http://www.elsevier.com/locate/withdrawalpolicy)). This article has been retracted at the request of the Editors. The authors have plagiarized part of a paper that had already appeared in J. Appl. Phys. 106, 093709 (2009); (10.1063/1.3256182) (6 pages): Title: Effects of pressure on charge transport and magnetic properties of La1.32Sr1.68Mn2O7 layered manganite by M. Kumaresavanji, M. S. Reis, Y. T. Xing, and M. B. Fontes. One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not appeared in a publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process
[en] We study the transport properties of multiterminal graphene nanodevices using the Landauer-Buttiker approach and the tight binding model. We consider a four-terminal device made at the crossing of a zigzag and armchair nanoribbons and two types of T-junction devices. The transport properties of graphene multiterminal devices are highly sensitive to the details of the junction region. Thus the properties are drastically different from those on the armchair and zigzag counterparts. In the cross-junction device, we see a conductance dip in the armchair lead associated with a conductance peak in the zigzag lead. We find that this effect is enhanced in a T-junction device with one armchair sidearm