First-Principles Study on Electron-Conduction Properties of C60_{60} Chains

The electron-conduction properties of fullerene chains are examined by first-principles calculations based on the density functional theory. The conductivity of the C$_{60}$ dimer is low owing to the constraint of the junction of the molecules on electron conduction, whereas the C$_{60}$ monomer exhibits a conductance of $\sim$ 1 G$_0$. One of the three degenerate $t_{u1}$ states of C$_{60}$ is relevant to conduction and the contributions of the others are small. In addition, we found a more interesting result that the conductance of the fullerene chain is drastically increased by encapsuling metal atoms into cages.Comment: 10pages and 5 figure

Magnetic orderings in Al nanowires suspended between electrodes

A theoretical analysis of a relation between atomic and spin-electronic structures for the ground state of single-row aluminum nanowires suspended between Al(001) electrodes is demonstrated using first-principles molecular-dynamics simulations. We obtain a unusual result that a 3-aluminum-atom nanowire sandwiched between the electrodes does not manifest magnetic ordering although an isolated aluminum trimer molecule in a straight line is spin-polarized. On the other hand, a 5-atom nanowire exhibits ferromagnetic ordering, where three central atoms form a spin-polarized trimer. Moreover, in the case of an 8-atom nanowire, the middle atoms in the nanowire form two spin-polarized trimers with antiferromagnetic ordering.Comment: 9 page

New structural model for GeO2/Ge interface: A first-principles study

First-principles modeling of a GeO2/Ge(001) interface reveals that sixfold GeO2, which is derived from cristobalite and is different from rutile, dramatically reduces the lattice mismatch at the interface and is much more stable than the conventional fourfold interface. Since the grain boundary between fourfold and sixfold GeO2 is unstable, the sixfold GeO2 forms a large grain at the interface. On the contrary, a comparative study with SiO2 demonstrates that SiO2 maintains a fourfold structure. The sixfold GeO2/Ge interface is shown to be a consequence of the ground-state phase of GeO2. In addition, the electronic structure calculation reveals that sixfold GeO2 at the interface shifts the valence band maximum far from the interface toward the conduction band.Comment: 18 pages, 5 figures, and 2 table

Novel time-saving first-principles calculation method for electron-transport properties

We present a time-saving simulator within the framework of the density functional theory to calculate the transport properties of electrons through nanostructures suspended between semi-infinite electrodes. By introducing the Fourier transform and preconditioning conjugate-gradient algorithms into the simulator, a highly efficient performance can be achieved in determining scattering wave functions and electron-transport properties of nanostructures suspended between semi-infinite jellium electrodes. To demonstrate the performance of the present algorithms, we study the conductance of metallic nanowires and the origin of the oscillatory behavior in the conductance of an Ir nanowire. It is confirmed that the $s$-$d_{z^2}$ channel of the Ir nanowire exhibits the transmission oscillation with a period of two-atom length, which is also dominant in the experimentally obtained conductance trace

Fully spin-dependent transport of triangular graphene flakes

The magnetic moment and spin-polarized electron transport properties of triangular graphene flakes surrounded by boron nitride sheets (BNC structures) are studied by using first-principles calculations based on density functional theory. Their dependence on the BNC structure is discussed, revealing that small isolated graphene flakes have large magnetic moment. When the BNC structure is suspended between graphene electrodes, the spin-polarized charge density distribution accumulates at the edge of the graphene flakes and no spin polarization is observed in the graphene electrodes. We also found that the BNC structure demonstrates perfectly spin-polarized transport properties in the wide energy window around the Fermi level. Our first-principles results indicate that the BNC structure provides new possibilities to electrically control spin

First-principles calculation method for electron transport based on grid Lippmann-Schwinger equation

We develop a first-principles electron-transport simulator based on the Lippmann--Schwinger (LS) equation within the framework of the real-space finite-difference scheme. In our fully real-space based LS (grid LS) method, the ratio expression technique for the scattering wave functions and the Green's function elements of the reference system is employed to avoid numerical collapse. Furthermore, we present analytical expressions and/or prominent calculation procedures for the retarded Green's function, which are utilized in the grid LS approach. In order to demonstrate the performance of the grid LS method, we simulate the electron-transport properties of the semiconductor/oxide interfaces sandwiched between semi-infinite metal electrodes. The results confirm that the leakage current through the (001)Si/SiO$_2$ model becomes much larger when the dangling-bond (DB) state is induced by a defect in the oxygen layer while that through the (001)Ge/GeO$_2$ model is insensitive to the DB state

First-principles calculation of electronic polarization of III-V nanotubes

A first-principles study of the electronic polarization of BN and AlN nanotubes and their graphitic sheets under an external electric field has been performed. We found that the polarization per atom of zigzag nanotubes increases with decreasing diameter while that of armchair nanotubes decreases. The variation of the polarization is related to the exterior angle of the bonds around the B or Al atoms rather than that around the N atoms. The increase in the polarization of the zigzag nanotubes with decreasing diameter is caused by the large variation of the exterior angle when they are wrapped into the tubular form. On the other hand, the decrease in the bond length results in the weak polarization of thin armchair nanotubes.Comment: 12 pages. to be published in Phys. Rev.

First-principles study on dielectric properties of NaCl crystal and ultrathin NaCl films under finite external electric field

We present a first-principles study on the dielectric properties of an NaCl crystal and ultrathin NaCl films under a finite external electric field. Our results show that the high-frequency dielectric constant of the films is not affected by the finite size effect from crystal surfaces and is close to that of the crystal, whereas the static one is sensitive to the thickness of the film due to the difference in the atomic configurations between the surface and inside of the film.Comment: 11 pages and 4 figure

Effect of Particle Properties on Fluidized Powder Conveying in a Horizontal Channel

AbstractThis study experimentally investigated the dense phase pneumatic conveying in a horizontal rectangular channel using the fluidizing air. The powder used the glass beads belongs to Geldart B particle, where the mean particle diameter is 127μm, the particle density is 2623kg/m3 and the minimum fluidizing velocity is 12.3mm/s. The experimental device consists of a powder discharge vessel, a horizontal rectangular channel at the side of vessel and the air supply section at the bottom of the vessel and the horizontal channel. The powder was fluidized by air through the porous membrane of the air supply section at the bottom of the vessel and the horizontal channel. Then, this system can be conveyed the fluidized powder. As the result, we confirmed the requirement that the fluidizing air to the bottom of the powder discharge vessel was required to the powder conveying of this system, and that the fluidizing velocity at the bottom of the horizontal channel was larger than that of the minimum fluidizing velocity. This result means that the fluidizing velocity at the bottom of the vessel and the horizontal channel is important to obtain the stable powder conveying. The mass flow rate and solid loading ratio were estimated by the measured data of the mass of transported powder. In addition, these results were compared with the conveying characteristic of the glass beads of 53μm belongs to Geldart A particle. Then, the mass flow rate of Geldart A particle was higher than that of Geldart B particle. The solid loading ratio of the Geldart A particle was also greatly large to that of Geldart B particle. Therefore, we considered that the high conveying efficiency to Geldart A particle was obtained, when the dimensionless fluidizing velocities at the bottom of the powder discharge vessel and the horizontal channel were same condition