One-Dimensional Transition Metal-Benzene Sandwich Polymers: Possible Ideal Conductors for Spin Transport

We investigate the electronic and magnetic properties of the proposed one-dimensional transition metal (TM=Sc, Ti, V, Cr, and Mn)-benzene (Bz) sandwich polymers by means of density functional calculations. [V(Bz)]$_{\infty}$ is found to be a quasi-half-metallic ferromagnet and half-metallic ferromagnetism is predicted for [Mn(Bz)]$_{\infty}$. Moreover, we show that stretching the [TM(Bz)]$_{\infty}$ polymers could have dramatic effects on their electronic and magnetic properties. The elongated [V(Bz)]$_{\infty}$ displays half-metallic behavior, and [Mn(Bz)]$_{\infty}$ stretched to a certain degree becomes an antiferromagnetic insulator. The possibilities to stabilize the ferromagnetic order in [V(Bz)]$_{\infty}$ and [Mn(Bz)]$_{\infty}$ polymers at finite temperature are discussed. We suggest that the hexagonal bundles composed by these polymers might display intrachain ferromagnetic order at finite temperature by introducing interchain exchange coupling

Electronic, Mechanical, and Piezoelectric Properties of ZnO Nanowires

Hexagonal [0001] nonpassivated ZnO nanowires are studied with density functional calculations. The band gap and Young's modulus in nanowires which are larger than those in bulk ZnO increase along with the decrease of the radius of nanowires. We find ZnO nanowires have larger effective piezoelectric constant than bulk ZnO due to their free boundary. In addition, the effective piezoelectric constant in small ZnO nanowires doesn't depend monotonously on the radius due to two competitive effects: elongation of the nanowires and increase of the ratio of surface atoms

All-Optical Spiking Neuron Based On Passive Micro-Resonator

Neuromorphic photonics that aims to process and store information simultaneously like human brains has emerged as a promising alternative for the next generation intelligent computing systems. The implementation of hardware emulating the basic functionality of neurons and synapses is the fundamental work in this field. However, previously proposed optical neurons implemented with SOA-MZIs, modulators, lasers or phase change materials are all dependent on active devices and quite difficult for integration. Meanwhile, although the nonlinearity in nanocavities has long been of interest, the previous theories are intended for specific situations, e.g., self-pulsation in microrings, and there is still a lack of systematic studies in the excitability behavior of the nanocavities including the silicon photonic crystal cavities. Here, we report for the first time a universal coupled mode theory model for all side-coupled passive microresonators. Attributed to the nonlinear excitability, the passive microresonator can function as a new type of all-optical spiking neuron. We demonstrate the microresonator-based neuron can exhibit the three most important characteristics of spiking neurons: excitability threshold, refractory period and cascadability behavior, paving the way to realize all-optical spiking neural networks.Comment: 8 pages, 7 figure

Linear scaling calculation of band edge states and doped semiconductors

Linear scaling methods provide total energy, but no energy levels and canonical wavefuctions. From the density matrix computed through the density matrix purification methods, we propose an order-N (O(N)) method for calculating both the energies and wavefuctions of band edge states, which are important for optical properties and chemical reactions. In addition, we also develop an O(N) algorithm to deal with doped semiconductors based on the O(N) method for band edge states calculation. We illustrate the O(N) behavior of the new method by applying it to boron nitride (BN) nanotubes and BN nanotubes with an adsorbed hydrogen atom. The band gap of various BN nanotubes are investigated systematicly and the acceptor levels of BN nanotubes with an isolated adsorbed H atom are computed. Our methods are simple, robust, and especially suited for the application in self-consistent field electronic structure theory

Linear scaling calculation of maximally-localized Wannier functions with atomic basis set

We have developed a linear scaling algorithm for calculating maximally-localized Wannier functions (MLWFs) using atomic orbital basis. An O(N) ground state calculation is carried out to get the density matrix (DM). Through a projection of the DM onto atomic orbitals and a subsequent O(N) orthogonalization, we obtain initial orthogonal localized orbitals. These orbitals can be maximally localized in linear scaling by simple Jacobi sweeps. Our O(N) method is validated by applying it to water molecule and wurtzite ZnO. The linear scaling behavior of the new method is demonstrated by computing the MLWFs of boron nitride nanotubes.Comment: J. Chem. Phys. in press (2006

Country Image, e-WOM and Purchase Intention of Korean Products in China——With Korean Cosmetic Products as an Example

Country image is viewed as the overall perception of consumers from a particular country, based on their prior perception of the country’s production and marketing strengths and weaknesses and this image affect customer attitudes like purchase intention. The purpose of our study was to develop and validate the relationship among country image, e-WOM and purchase intention of foreign products. Based on literatures, a comprehensive set of constructs and hypotheses was compiled with a methodology for testing them. A questionnaire was constructed and data were collected from 255 customers in Beijing and Shanghai. The results indicated that country image affect purchase intention of Korean Cosmetic products through e-WOM

Electron-Phonon Coupling in Boron-Doped Diamond Superconductor

The electronic structure, lattice dynamics, and electron-phonon coupling of the boron-doped diamond are investigated using the density functional supercell method. Our results indicate the boron-doped diamond is a phonon mediated superconductor, con rming previous theoretical conclusions deduced from the calculations employing the virtual crystal approximation. We show that the optical phonon modes involving B vibrations play an important role in the electron-phonon coupling. Di erent from previous theoretical results, our calculated electron-phonon coupling constant is 0.39 and the estimated superconducting transition temperature Tc is 4.4 K for the boron doped diamond with 2.78% boron content using the Coulomb pseudopotential \mu*= 0.10, in excellent agreement with the experimental result.Comment: 11 pages, 4 figures, Accepted by PR