Transport properties of poly(GACT)-poly(CTGA) deoxyribonucleic acid: A ladder model approach

In this paper, based on the tight-binding Hamiltonian model and within the framework of a generalized Green’s function technique, the electronic conduction through the poly(GACT)-poly(CTGA) DNA molecule in SWNT/DNA/SWNT structure has been numerically investigated. In a ladder model, we consider DNA as a planar molecule containing M cells and four further sites (two base pair sites and two backbone sites) in each cell, sandwiched between two semi-infinite single-walled carbon nanotubes (SWNT) as the electrodes. Having relied on Landauer formalism, we focussed on studying the current-voltage characteristics of DNA, the effect of the coupling strength of SWNT/DNA interface and the role of tube radius of nanotube contacts on the electronic transmission through the foregoing structure. Finally, a characteristic time was calculated for the electron transmission, which measures the delay caused by the tunnelling through the SWNT/DNA interface. The results clearly show that the calculated characteristic time and also the conductance of the system are sensitive to the coupling strength between DNA molecule and nanotube contacts.     

Electron transport through SWNT/<Emphasis Type="Italic">trans</Emphasis>-PA/SWNT structure (the role of solitons): A t-matrix technique

Using a tight-binding model and a transfer-matrix technique, we numerically investigate the effects of the coupling strength and the role of solitons on the electronic transmission through a system in which trans-polyacetylene (trans-PA) molecule is sandwiched between two semi-infinite single-walled carbon nanotubes (SWNT). We rely on Landauer formalism as the basis for studying the conductance properties of this system. Our calculations show that the solitons play an important role in the response of this system causing a large enhancement in the conductance. Also our results suggest that the conductance is sensitive to the CNT/molecule coupling strength.      

Dipolar Bose–Einstein condensate soliton on a two-dimensional optical lattice

Using a three-dimensional mean-field model we study one-dimensional dipolar Bose–Einstein condensate (BEC) solitons on a weak two-dimensional (2D) square and triangular optical lattice (OL) potentials placed perpendicular to the polarization direction. The stabilization against collapse and expansion of these solitons for a fixed dipolar interaction and a fixed number of atoms is possible for short-range atomic interaction lying between two critical limits. The solitons collapse below the lower limit and escapes to infinity above the upper limit. One can also stabilize identical tiny BEC solitons arranged on the 2D square OL sites forming a stable 2D array of interacting droplets when the OL sites are filled with a filling factor of 1/2 or less. Such an array is unstable when the filling factor is made more than 1/2 by occupying two adjacent sites of OL. These stable 2D arrays of dipolar superfluid BEC solitons are quite similar to the recently studied dipolar Mott insulator states on 2D lattice in the Bose–Hubbard model by Capogrosso-Sansone et al. [B. Capogrosso-Sansone, C. Trefzger, M. Lewenstein, P. Zoller, G. Pupillo, Phys. Rev. Lett. 104 (2010) 125301].     

Influence of soliton distributions on the spin-dependent electronic transport through polyacetylene molecule

In this paper, a detailed numerical study of the role of selected soliton distributions on the spin-dependent transport through trans-polyacetylene (PA) molecule is presented. The molecule is attached symmetrically to magnetic semi-infinite three-dimensional electrodes. Based on Su– Schrieffer–Heeger (SSH) Hamiltonian and using a generalized Green’s function formalism, we calculate the spin-dependent currents, the electronic transmission and tunnelling magnetoresistance (TMR). We found that the presence of a uniform distribution of the soliton centres along the molecular chain reduced the size of the band gap of trans-PA molecule. Moreover, a sublattice of the correlated solitons as binary clusters, which are randomly distributed along the chain, can induce extended electronic states in the band gap of the molecule. In this case, the band gap of the molecule is suppressed and at lower voltages, the TMR bandwidth is narrowed. The current–voltage characteristic then shows an ohmic-like behaviour.     

Electronic transport in double-strand poly(dG)-poly(dC) DNA segments

We study the electronic properties of a double-strand quasiperiodic DNA molecule modeled by a one-dimensional effective Hamiltonian, which includes contributions from the nucleobasis system as well as the sugar-phosphate backbone. Our theoretical approach makes use of Dyson's equation together with a transfer-matrix treatment, considering an electronic tight-binding Hamiltonian model to investigate the electronic density of states (DOS) and the electronic transmissivity of sequences of DNA finite segments. To mimic the DNA segments, we consider the finite quasiperiodic sequences of Fibonacci's type, in a poly(dG)-poly(dC) configuration, whose building blocks are the bases guanine G and cytosine C. We compared the electronic transport found for the quasiperiodic structure to those using a sequence of natural DNA, as part of the human chromosome Ch22.     

金属/C2H2/金属结构中的电子输运

在紧束缚近似下,利用转移矩阵法对“金属/C2H2/金属”结构的分子导线的电子输运性质进行了研究。通过转移矩阵法求出转移矩阵和散射矩阵,从而解析地得到体系的透射系数和态密度的变化,并详细分析了透射系数对C2H2与金属的耦合强度及两个(CH)间的耦合强度的依赖关系。我们的结果显示这种结构的分子导线有着较好的开关特性。     

Mathematical modeling of photoisomerization with intramolecular proton transfer

A system of equations describing time changes in the matrix elements of the density operator of a seven-level model of a molecule interacting with a light pulse taking into account spontaneous (including collective) decays of molecule excited states is suggested. Model parameters were selected to allow us to perform modeling of the photoisomerization of a molecule with two isomeric states with different stable proton positions on an intramolecular H-bond by numerically solving the suggested system of equations for density operator matrix elements. An analysis of the characteristic time dependences of the population of states of the model under consideration showed that proton phototransfer in the collective decay of various isomeric states of a molecule in an excited electronic state can be one of effective mechanisms of the photoisomerization of molecules whose structure is described by the model.     

Inverse oxide/metal catalysts: A versatile approach for activity tests and mechanistic studies

There is a general desire to improve the configuration of industrial catalysts to take advantage of the intrinsic properties of metal oxides. In recent years, a series of studies has been published examining the growth of oxide nanoparticles on metal substrates. These studies have revealed structures for the supported oxide which are different from those found in bulk phases. In addition, the oxide ? metal interactions can alter the electronic states of the oxide producing new chemical properties. On an inverse oxide/metal catalyst, the reactants can interact with defect sites of the oxide nanoparticles, metal sites, and the metal–oxide interface. In these systems, one can couple the special reactivity of the oxide nanoparticles to the reactivity of the metal to obtain high catalytic activity. Furthermore, an oxide/metal system is also an attractive model for fundamental studies. It can be used to investigate the role of the oxide in a catalytic process, and how the stability of different reaction intermediates depends on the nature of the oxide.     

Double-exchange model for molecule-based magnets

We report a detailed study of a double-exchange model proposed for the molecule-based magnets. The model is applied to a two-dimensional periodic complex made of a transition metal and an organic molecule in which the electronic structure is described by effective d orbitals of the transition metal ion at infinite Hund's coupling limit and the lowest unoccupied molecular orbital of the organic molecule, π^∗. Depending on the average electron density of the organic molecules and various superexchange couplings between metal ions' core spins, magnetic states of the complex are investigated. Performing Monte Carlo calculations on a model Hamiltonian for various electron densities of the organic molecule, the average magnetization and critical magnetic ordering temperatures are determined.     

Electronic States and Schottky Barrier Height at Metal/MgO(100) Interfaces

Using an ab initio total energy approach, we study the electronic structure of metal/MgO(100) interfaces. By considering simple and transition metals, different adsorption sites and different interface separations, we analyze the influence of the character of metal and of the detailed interfacial atomic structure. We calculate the interface density of states, electron transfer, electric dipole, and the Schottky barrier height. We characterize three types of electronic states: states due to chemical bonding which appear at well defined energies, conventional metal-induced gap states associated to a smooth density of states in the MgO gap region, and metal band distortions due to polarization by the electrostatic field of the ionic substrate. We point out that, with respect to the extended Schottky limit, the interface formation yields an electric dipole mainly determined by the substrate characteristics. Indeed, the metal-dependent contributions (interfacial states and electron transfer) remain small with respect to the metal polarization induced by the substrate electrostatic field.     

Observation of a discrete family of dissipative solitons in a nonlinear optical system

We report on the observation of a discrete family of spatial dissipative solitons in a simple optical pattern forming system, which is based on a modified single-mirror feedback arrangement. After a pitchfork bifurcation the system possesses two (nearly) equivalent coexisting states of different polarizations. The spatial solitons correspond to excursions from one of the two states serving as a background state towards the other one. The members of the soliton family differ in the number of high-amplitude radial oscillations. The observations are in good agreement with numerical simulations and general expectations for dissipative solitons.     

Non-linear transport by solitons in nanofibers of polymers in high magnetic field

Nonlinear local excitations like solitons, polarons, and bipolarons are known to be responsible for physical properties of conducting polymers. Recent experiments on nano-fibers in high electric and magnetic fields provide a further insight by demonstrating an effect of vanishing magnetoconductance (MC) in the polyacetylene (PA)—in contrast to other polymers. Here we present new experimental data and describe the theoretical model based on notion of solitons—dimerization kinks which can carry either the spin or the charge; they are allowed only in the PA with its degenerate ground state. The solitons experience a confinement force due to the interchange coupling which is erased by the electric field and disappears above critical field strength. The unbinding by tunneling allows for the transport of individual solitons, which sweeps off the spins residing at electronic intragap states associated with polarons, hence the vanishing MC.     

Mass-selected Ag<Subscript>3</Subscript> clusters soft-landed onto MgO/Mo(100): femtosecond photoemission and first-principles simulations

The electronic structure of supported mass-selected Ag₃ clusters is analyzed by joint femtosecond photoemission spectroscopy and ab initio theoretical investigations. A wide band gap insulating magnesia ultra-thin film on Mo(100) has been chosen as substrate in order to minimize the electronic interaction between metal clusters and support. After magnesia ultra-thin film preparation no photoemission from the molybdenum substrate is observed anymore, instead very weak two photon photoemission is detected possibly originating from surface or subsurface oxide defect states. Soft-landing deposition of 2 of atomic monolayer equivalents of Ag₃ clusters results in the disappearance also of the MgO two photon photoemission signal, while a strong single photon photoemission signal is detected from states located directly below the Fermi level. The theoretical study of structural, electronic and optical properties of Ag₃ at two model sites of MgO (100), the stoichiometric MgO(100) and an F_S-center defect, based on the DFT method and the embedded cluster model provides insight into the interactions between the cluster and the support which are responsible for the characteristic spectroscopic features.     

Multidimensional solitons: Well-established results and novel findings

A brief review is given of some well-known and some very recent results obtained in studies of two- and three-dimensional (2D and 3D) solitons. Both zero-vorticity (fundamental) solitons and ones carrying vorticity S = 1 are considered. Physical realizations of multidimensional solitons in atomic Bose-Einstein condensates (BECs) and nonlinear optics are briefly discussed too. Unlike 1D solitons, which are typically stable, 2D and 3D ones are vulnerable to instabilities induced by the occurrence of the critical and supercritical collapse, respectively, in the same 2D and 3D models that give rise to the solitons. Vortex solitons are subject to a still stronger splitting instability. For this reason, a central problem is looking for physical settings in which 2D and 3D solitons may be stabilized. The review specifically addresses one well-established topic, viz., the stabilization of the 3D and 2D states, with S = 0 and 1, trapped in harmonic-oscillator (HO) potentials, and another topic which was developed very recently: the stabilization of 2D and 3D free-space solitons, which mix components with S = 0 and ± 1 (semi-vortices and mixed modes), in a binary system with the (pseudo-) spin-orbit coupling (SOC) between its components. The former model is based on the single cubic nonlinear Schrödinger/Gross-Pitaevskii equation (NLSE/GPE), while the latter one is represented by a system of two coupled GPEs. In both cases, the generic situations are drastically different in the 2D and 3D geometries. In the 2D settings, the stabilization mechanism creates a stable ground state (GS, which was absent without it), whose norm falls below the threshold value at which the critical collapse sets in. In the 3D geometry, the supercritical collapse does not allow to create a GS, but metastable solitons can be constructed.     

Recovering pure states in two-state quantum systems

In this work, we study the loss and recovery of pure states (i.e., coherence) in two-state molecules and quantum dots. The molecules of two electronic states and a one-dimensional nuclear vibration are modeled by a quantum–classical dynamical model. According to the simulations, pure states of a two-state molecule can be restored by the excitation of the nuclear vibration by a well-defined electromagnetic field. In the case of a quantum dot, pure states can be regained through the modulation of the energy levels through the application of a proper bias voltage on the dot.     

Topologically protected edge gap solitons of interacting Bosons in one-dimensional superlattices

We comprehensively investigate the nontrivial states of an interacting Bose system in a cosine potential under the open boundary condition. Our results show that there exists a kind of stable localized state: edge gap solitons. We argue that the states originate from the eigenstates of independent edge parabolas. In particular, the edge gap solitons exhibit a nonzero topological-invariant behavior. The topological nature is due to the connection of the present model to the quantized adiabatic particle transport problem. In addition, the composition relations between the gap solitons and the extended states are also discussed.     

碱基序列对DNA分子电子结构的影响

将DNA分子看成一维二元随机序列，利用负本征值理论计算其态密度，针对碱基对分布和相对含量等参量，讨论了DNA分子的电子结构.结果表明碱基对分布和相对含量都对电子能态结构影响较大，说明碱基序列对DNA分子的电子结构影响很大. 关键词： DNA分子 电子态密度 碱基对     

Solitons in semiconductor microstructures with a two-dimensional electron gas

Nonlinear waves in a two-dimensional electronic plasma with metal screening gates are investigated. It is shown that solitons described by the KdV equation exist in such a system. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 7, 479–481 (10 October 1999)     

Degeneracy of solitons and polarons in polyacetylene for translation between nearest neighbour sites

In polyacetylene, there are solitons with two different interface natures, one connecting oppositely dimerized chains by two single bonds and another by two double bonds. There are also polarons of two kinds, one with the center on a double bond and another on a single bond. These two kinds of solitons and polarons are converted to each other by translation between nearest neighbour sites. They have apparently different electronic structures but are degenerate in energy and have the same lattice structure. The origin of the degeneracy is disclosed.