48 research outputs found

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

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    The electron-conduction properties of fullerene chains are examined by first-principles calculations based on the density functional theory. The conductivity of the C60_{60} dimer is low owing to the constraint of the junction of the molecules on electron conduction, whereas the C60_{60} monomer exhibits a conductance of \sim 1 G0_0. One of the three degenerate tu1t_{u1} states of C60_{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

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

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    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 ss-dz2d_{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

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

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    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/SiO2_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/GeO2_2 model is insensitive to the DB state

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

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    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

    First-principles transport calculation method based on real-space finite-difference nonequilibrium Green's function scheme

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    We demonstrate an efficient nonequilibrium Green's function transport calculation procedure based on the real-space finite-difference method. The direct inversion of matrices for obtaining the self-energy terms of electrodes is computationally demanding in the real-space method because the matrix dimension corresponds to the number of grid points in the unit cell of electrodes, which is much larger than that of sites in the tight-binding approach. The procedure using the ratio matrices of the overbridging boundary-matching technique [Phys. Rev. B {\bf 67}, 195315 (2003)], which is related to the wave functions of a couple of grid planes in the matching regions, greatly reduces the computational effort to calculate self-energy terms without losing mathematical strictness. In addition, the present procedure saves computational time to obtain Green's function of the semi-infinite system required in the Landauer-B\"uttiker formula. Moreover, the compact expression to relate Green's functions and scattering wave functions, which provide a real-space picture of the scattering process, is introduced. An example of the calculated results is given for the transport property of the BN ring connected to (9,0) carbon nanotubes. The wave function matching at the interface reveals that the rotational symmetry of wave functions with respect to the tube axis plays an important role in electron transport. Since the states coming from and going to electrodes show threefold rotational symmetry, the states in the vicinity of the Fermi level, whose wave function exhibits fivefold symmetry, do not contribute to the electron transport through the BN ring.Comment: 34 page

    First-principles study on scanning tunneling microscopy images of hydrogen-terminated Si(110) surfaces

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    Scanning tunneling microscopy images of hydrogen-terminated Si(110) surfaces are studied using first-principles calculations. Our results show that the calculated filled-state images and local density of states are consistent with recent experimental results, and the empty-state images appear significantly different from the filled-state ones. To elucidate the origin of this difference, we examined in detail the local density of states, which affects the images, and found that the bonding and antibonding states of surface silicon atoms largely affect the difference between the filled- and empty-state images.Comment: 4 pages, and 4 figure
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