Conformation dependence of charge transfer and level alignment in nitrobenzene junctions with pyridyl anchor groups

The alignment of molecular levels with the Fermi energy in single molecule junctions is a crucial factor in determining their conductance or the observability of quantum interference effects. In the present study which is based on density functional theory calculations, we explore the zero-bias charge transfer and level alignment for nitro-bipyridyl-phenyl adsorbed between two gold surfaces which we find to vary significantly with the molecular conformation. The net charge transfer is the result of two opposing effects, namely Pauli repulsion at the interface between the molecule and the leads, and the electron accepting nature of the NO$_2$ group, where only the latter which we analyze in terms of the electronegativity of the isolated molecules depends on the two intra-molecular torsion angles. We provide evidence that the conformation dependence of the alignment of molecular levels and peaks in the transmission function can indeed be understood in terms of charge transfer for this system, and that other properties such as molecular dipoles do not play a significant role. Our study is relevant for device design in molecular electronics where nitrobenzene appears as a component in proposals for rectification, quantum interference or chemical gating.Comment: 10 pages, 6 figure

Contact Dependence of Carrier Injection in Carbon Nanotubes: An Ab Initio Study

We combine ab initio density functional theory with transport calculations to provide a microscopic basis for distinguishing between good and poor metal contacts to nanotubes. Comparing Ti and Pd as examples of different contact metals, we trace back the observed superiority of Pd to the nature of the metal-nanotube hybridization. Based on large scale Landauer transport calculations, we suggest that the `optimum' metal-nanotube contact combines a weak hybridization with a large contact length between the metal and the nanotube.Comment: final version, including minor corrections by edito

Liquid markets and market liquids: collective and single-asset dynamics in financial markets

We characterize the collective phenomena of a liquid market. By interpreting the behavior of a no-arbitrage N asset market in terms of a particle system scenario, (thermo)dynamical-like properties can be extracted from the asset kinetics. In this scheme the mechanisms of the particle interaction can be widely investigated. We test the verisimilitude of our construction on two-decade stock market daily data (DAX30) and show the result obtained for the interaction potential among asset pairs.Comment: 4 pages, svjour.cls, 3 figures, to appear in The European Physical Journal

Effective models for charge transport in DNA nanowires

The rapid progress in the field of molecular electronics has led to an increasing interest on DNA oligomers as possible components of electronic circuits at the nanoscale. For this, however, an understanding of charge transfer and transport mechanisms in this molecule is required. Experiments show that a large number of factors may influence the electronic properties of DNA. Though full first principle approaches are the ideal tool for a theoretical characterization of the structural and electronic properties of DNA, the structural complexity of this molecule make these methods of limited use. Consequently, model Hamiltonian approaches, which filter out single factors influencing charge propagation in the double helix are highly valuable. In this chapter, we give a review of different DNA models which are thought to capture the influence of some of these factors. We will specifically focus on static and dynamic disorder.Comment: to appear in "NanoBioTechnology: BioInspired device and materials of the future". Edited by O. Shoseyov and I. Levy. Humana Press (2006

Conductance of a molecular wire attached to mesoscopic leads: contact effects

We study linear electron transport through a molecular wire sandwiched between nanotube leads. We show that the presence of such electrodes strongly influences the calculated conductance. We find that depending on the quality and geometry of the contacts between the molecule and the tubular reservoirs, linear transport can be tuned between an effective Newns spectral behavior and a more structured one. The latter strongly depends on the topology of the leads. We also provide analytical evidence for an anomalous behavior of the conductance as a function of the contact strength.Comment: 5 pages, 1 figure, to appear in Acta Physica Polonica

Sum rule for transport in a Luttinger liquid with long range interaction in the presence of an impurity

We show that the non-linear dc transport in a Luttinger liquid with interaction of finite range in the presence of an impurity is governed by a sum rule which causes the charging energy to vanish.Comment: 5 pages, RevTeX, 1 figure, to be published in Europhysics Letter

A pure-carbon ring transistor: The role of topology and structure

We report results on the rectification properties of a carbon nanotube (CNT) ring transistor, contacted by CNT leads, whose novel features have been recently communicated by Watanabe et al. [Appl. Phys. Lett. 78, 2928 (2001)]. This paper contains results which are validated by the experimental observations. Moreover, we report on additional features of the transmission of this ring device which are associated with the possibility of breaking the lead inversion symmetry. The linear conductance displays a "chessboard"-like behavior alternated with anomalous zero-lines which should be directly observable in experiments. We are also able to discriminate in our results structural properties (quasi-onedimensional confinement) from pure topological effects (ring configuration), thus helping to gain physical intuition on the rich ring phenomenology.Comment: 3 pages, 4 figure

Mechanical properties and thermal conductivity of graphitic carbon nitride: A molecular dynamics study

Graphitic carbon nitride nanosheets are among 2D attractive materials due to presenting unusual physicochemical properties.Nevertheless, no adequate information exists about their mechanical and thermal properties. Therefore, we used classical molecular dynamics simulations to explore the thermal conductivity and mechanical response of two main structures of single-layer triazine-basedg-C3N4 films.By performing uniaxial tensile modeling, we found remarkable elastic modulus of 320 and 210 GPa, and tensile strength of 47 GPa and 30 GPa for two different structures of g-C3N4sheets. Using equilibrium molecular dynamics simulations, the thermal conductivity of free-standing g-C3N4 structures were also predicted to be around 7.6 W/mK and 3.5 W/mK. Our study suggests the g-C3N4films as exciting candidate for reinforcement of polymeric materials mechanical properties

The role of contacts in molecular electronics

Molecular electronic devices are the upmost destiny of the miniaturization trend of electronic components. Although not yet reproducible on large scale, molecular devices are since recently subject of intense studies both experimentally and theoretically, which agree in pointing out the extreme sensitivity of such devices on the nature and quality of the contacts. This chapter intends to provide a general theoretical framework for modelling electronic transport at the molecular scale by describing the implementation of a hybrid method based on Green function theory and density functional algorithms. In order to show the presence of contact-dependent features in the molecular conductance, we discuss three archetypal molecular devices, which are intended to focus on the importance of the different sub-parts of a molecular two-terminal setup.Comment: 17 pages, 8 figure

Spin dependent conductance of a quantum dot side attached to topological superconductors as a probe of Majorana fermion states

Spin-polarized transport through a quantum dot side attached to a topological superconductor and coupled to a pair of normal leads is discussed in Coulomb and Kondo regimes. For discussion of Coulomb range equation of motion method with extended Hubbard I approximation is used and Kondo regime is analyzed by Kotliar-Ruckenstein slave boson approach. Apart from the occurrence of zero bias anomaly the presence of Majorana states reflects also in splitting of Coulomb lines. In the region of Coulomb borders the spin dependent negative differential conductance is observed. Due to the low energy scale of Kondo effect this probe allows for detection of Majorana states even for extremely weak coupling with topological wire. In this range no signatures of Majorana states appear in Coulomb blockade dominated transport.Comment: 3 pages, 3 figure