197 research outputs found
First-Principles Study on Electron-Conduction Properties of C 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 dimer is low owing to the constraint of the
junction of the molecules on electron conduction, whereas the C monomer
exhibits a conductance of 1 G. One of the three degenerate
states of C 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 - 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 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
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
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