Search results for: Takahisa Ohno

Items from 1 to 20 out of 47 results

article

A first principles study on the CVD graphene growth on copper surfaces: A carbon atom incorporation to graphene edges

Nobuo Tajima, Tomoaki Kaneko, Jun Nara, Takahisa Ohno

Surface Science > 2016 > 653 > C > 123-129

Carbon atom reactions in the chemical vapor deposition (CVD) processes for graphene production on copper surfaces have been studied by first principles molecular dynamics (MD) simulations at a typical CVD growth temperature. This study focuses on the processes of a carbon atom incorporation to graphene edges. The energy barriers of these carbon atom incorporation reactions have been calculated as...

article

Spintronic Transport in Armchair Graphene Nanoribbon with Ferromagnetic Electrodes: Half-Metallic Properties

Hongmei Liu, Hisashi Kondo, Takahisa Ohno

Nanoscale Research Letters > 2016 > 11 > 1 > 1-8

Utilizing first-principles theory, we demonstrate that half-metallicity can be realized in a junction composed of non-magnetic armchair graphene nanoribbon (AGNR) and ferromagnetic Ni electrodes. The half-metallic property originates from the AGNR energy gap of the up spin located at the Fermi energy, while large electronic states are generated for the down spin. By altering the interlayer distance...

article

First-principles study on reconstruction of 4H-SiC(0001) and (0001¯)

Tomoaki Kaneko, Takahiro Yamasaki, Nobuo Tajima, Takahisa Ohno

Surface Science > 2016 > 647 > C > 45-50

We have found that 4H-SiC(0001) and (0001¯) surfaces can reconstruct to stable (2×1) π-bonded chain structures, which are the same kind of structure that was predicted by Pandey for Si(111) surface (K. C. Pandey, 1981) but have not been examined for the SiC surfaces so far. Their relative energy gain on (0001) and (0001¯) surfaces to the ideal spin non-polarized surfaces are 0.275–0.298eV/(1×1) and...

article

Synthesis, structure and ionic conductivities of novel Li-ion conductor A3LixTa6−xZrxSi4O26 (A=Sr and Ba)

Akihisa Aimi, Yoshiyuki Inaguma, Miki Kubota, Daisuke Mori, more

Solid State Ionics > 2016 > 285 > C > 19-28

The solid state oxide Li-ion conductors with high electrochemical stability as well as high ionic conductivity are needed for application to all-solid-state Li-ion battery. In this study, A₃Li_xTa_6−xZr_xSi₄O₂₆ (A=Sr and Ba) as the candidate solid electrolytes stable against Li metal were synthesized by a conventional solid state reaction, and their structure and ionic conductivities were investigated...

article

Theoretical insight into charging process in a Li3PO4 (100)/LiFePO4 (010) coherent interface system

Masato Sumita, Yoshinori Tanaka, Minoru Ikeda, Takahisa Ohno

Solid State Ionics > 2016 > 285 > C > 59-65

We have investigated the introduction of Li vacancy (V_Li^× in the Kröger–Vink notation) into a Li₃PO₄ (100)/LiFePO₄ (010) coherent interface with the density functional theory in order to gain an insight into the initial stage of the charging process. The V_Li^× introduction results in the formation of a Li ion vacancy (V_Li′) and hole (h). When one V_Li^× is introduced in each bulk LiFePO₄ and Li₃PO₄ materials...

article

In situ X-ray diffraction for millisecond-order dynamics of BaZrO3 nanoparticle formation in supercritical water

Akira Yoko, Makoto Akizuki, Naohisa Hirao, Shinji Kohara, more

The Journal of Supercritical Fluids > 2016 > 107 > C > 746-752

In situ high-energy X-ray diffraction measurements were conducted to elucidate the dynamics of barium zirconate (BaZrO₃) nanoparticle formation in supercritical water. Time-resolved experiments of approximately milliseconds were achieved using a continuous-flow reactor and high-energy X-ray diffraction, which allows us to probe the sample in a stainless-steel tube. The size and structure of BaZrO₃...

article

Visible light photoreactivity from hybridization states between carbon nitride bandgap states and valence states in Nb and Ti oxides

Hosik Lee, Takahisa Ohno

Chemical Physics > 2013 > 415 > Complete > 156-160

For better efficiency as photocatalysts, N-doping for visible light reactivity has been intensively studied in Lamellar niobic and titanic solid acids (HNb ₃ O ₈ , H ₂ Ti ₄ O ₉ ), and its microscopic structures have been debated in this decade. We calculate the layered solid acids’ structures and bandgaps. Bandgap reduction by carbon nitride adsorption in interlayer...

article

First-principles study of chlorine atom diffusion on Si(111)–5×5 reconstructed surfaces

Yusuke Asari, Jun Nara, Takahisa Ohno

Applied Surface Science > 2013 > 267 > Complete > 70-73

Diffusion mechanisms of Cl atom adsorbed on Si(111)–(5×5) reconstructed surfaces are investigated by means of the first-principles density functional calculations. We compare two diffusion models for Cl diffusion; one is simple atom hopping model and the other is SiCl complex diffusion one, which is originally proposed to explain the diffusion process for another halogen, F. The energy barrier for...

article

Contribution analysis of the van der Waals term on electronic structures of carbon related systems

Youky Ono, Takahisa Ohno

Applied Surface Science > 2013 > 267 > Complete > 173-176

Contribution of the van der Waals term in the electron densities and the band structures of covalent bonding one-dimensional networks are studied. Calculations are performed with self-consistently implemented nonlocal van der Waals density functional (vdW-DF) into a first principle program. Results indicate that the contribution of the van der Waals term on band structures qualitatively depends on...

article

Implementation of the DFT+U method and constrained DFT calculations for U and J within a pseudopotential formalism: Application to FeO and LaVO₃

Tomoyuki Hamada, Takahisa Ohno, Sadamich Maekawa

Journal of the Korean Physical Society > 2013 > 62 > 12 > 2155-2159

A first-principles density functional theory (DFT) + U method based on the pseudopotential (PP) method was developed to enable a-priori prediction of electronic structures of strongly-correlated electronic structure (SCES) systems. The method determines the radius of the localized electron orbitals of a SCES system and the Hubbard parameters U and J for the electrons and calculates the electronic...

chapter

Poster: Planewave-Based First-Principles MD Calculation on 80,000-node K-Computer

Akiyoshi Kurod, Kazuo Minami, Takahiro Yamasaki, Jun Nara, more

2012 SC Companion: High Performance Computing, Networking Storage and Analysis > 1491 - 1492

2012 SC Companion: High-Performance Computing, Networking, Storage and Analysis (SCC)

We show the efficiency of a first-principles electronic structure calculation code, PHASE on the massive-parallel super computer, K, which has 80,000 nodes. This code is based on plane-wave basis set, thus FFT routines are included. We succeeded in parallelization of FFT routines needed in our code by localizing each FFT calculation in small number of nodes, resulting in decreasing communication time...

article

Biwire structure of methanol inside carbon nanotubes

Yoshimichi Nakamura, Takahisa Ohno

Chemical Physics Letters > 2012 > 539-540 > Complete > 123-127

Methanol molecules inside carbon nanotubes open to a liquid methanol reservoir are studied by molecular dynamics simulations. The way of filling is explored for a wide range of tube diameter size, from a large one revealing a ‘bulk mode’ to a small one revealing a ‘monowire mode’, in which the molecules are hydrogen-bonded one-dimensionally. Stemming from the coexistence of the hydrophobic and the...

article

Structure of water confined inside carbon nanotubes and water models

Yoshimichi Nakamura, Takahisa Ohno

Materials Chemistry and Physics > 2012 > 132 > 2-3 > 682-687

We study the effect of different water models on molecular dynamics simulations of the water structures inside carbon nanotubes, employing not only the commonly used three- and four-site water models, but also the five-site model. The water structures induced by the spontaneous filling of the uncapped carbon nanotubes with the reservoir water are focused on to demonstrate the effect. It is found that...

article

Possibility of Gas Sensor Using Electronic Transport Properties of Iron−Porphyrin Molecular Junction System

Hisashi Kondo, Jun Nara, Takahisa Ohno

The Journal of Physical Chemistry C > 2011 > 115 > 14 > 6886 - 6892

article

Theoretical study on diffusion mechanism of fluorine atom adsorbed on Si(111) reconstructed surface

Yusuke Asari, Jun Nara, Takahisa Ohno

Surface Science > 2011 > 605 > 1-2 > 225-231

We study diffusion mechanisms of fluorine atom adsorbed on Si(111) reconstructed surface by means of the first-principles density functional calculation. Recently, it was revealed experimentally that the fluorine diffusion is assisted by extra silicon atoms diffusing freely on the surface, whereas the detailed mechanism of the Si assist has not been understood. We first investigate F atom adsorption...

article

Lattice parameter dependence of energy barriers of hydrogenation of ultra small carbon nanotubes

Roberto Scipioni, Takahisa Ohno

Chemical Physics Letters > 2010 > 492 > 4-6 > 263-265

We study via first principles molecular dynamics the dependence of the Free Energy barrier for the room temperature hydrogenation of the ultra small carbon nanotubes (4,0) and (5,0) on the lattice parameter along the tube axis. We find that upon stretching the tube (4,0) the energy barrier for the incorporation of hydrogen provided by approaching H ₂ molecules, undergoing dissociation, can...

article

Tautomerism in Reduced Pyrazinacenes

Roberto Scipioni, Mauro Boero, Gary J. Richards, Jonathan P. Hill, more

Journal of Chemical Theory and Computation > 2010 > 6 > 2 > 517 - 525

article

Investigation of the Mechanism of Adsorption of β-Nicotinamide Adenine Dinucleotide on Single-Walled Carbon Nanotubes

Roberto Scipioni, Martin Pumera, Mauro Boero, Yuji Miyahara, more

The Journal of Physical Chemistry Letters > 2010 > 1 > 1 > 122 - 125

article

First-principles supercell calculations for simulating a shallow donor state in Si

Takenori Yamamoto, Tsuyoshi Uda, Takahiro Yamasaki, Takahisa Ohno

Physics Letters A > 2009 > 373 > 43 > 3989-3993

We present first-principles simulations of As-doped Si carried out using several cubic supercells of up to 10 648 atoms. The 1s As donor level in each supercell splits into three states, which have A1, T2, and E symmetries, respectively. The 1s(A1) wavefunction is well converged in the largest cell, and its spread is close to those of the effective-mass theories. However, the calculated binding energies...

article

Hydrogenation of ultrasmall carbon nanotubes: A first principle study

Roberto Scipioni, Mauro Boero, Takahisa Ohno

Chemical Physics Letters > 2009 > 480 > 4-6 > 215-219

We analyze, via molecular dynamics, the hydrogenation of the smallest zigzag and armchair carbon nanotubes. These tubes with radii smaller than 0.4nm, contrary to larger tubes, upon exposure to molecular hydrogen have an exothermic hydrogenation. First principles simulations show that these tubes are thermally stable up to temperatures of 1500K. The free energy profiles for hydrogen abstraction, computed...

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Search results for: Takahisa Ohno

A first principles study on the CVD graphene growth on copper surfaces: A carbon atom incorporation to graphene edges

Spintronic Transport in Armchair Graphene Nanoribbon with Ferromagnetic Electrodes: Half-Metallic Properties

First-principles study on reconstruction of 4H-SiC(0001) and (0001¯)

Synthesis, structure and ionic conductivities of novel Li-ion conductor A3LixTa6−xZrxSi4O26 (A=Sr and Ba)

Theoretical insight into charging process in a Li3PO4 (100)/LiFePO4 (010) coherent interface system

In situ X-ray diffraction for millisecond-order dynamics of BaZrO3 nanoparticle formation in supercritical water

Visible light photoreactivity from hybridization states between carbon nitride bandgap states and valence states in Nb and Ti oxides

First-principles study of chlorine atom diffusion on Si(111)–5×5 reconstructed surfaces

Contribution analysis of the van der Waals term on electronic structures of carbon related systems

Implementation of the DFT+U method and constrained DFT calculations for U and J within a pseudopotential formalism: Application to FeO and LaVO₃

Poster: Planewave-Based First-Principles MD Calculation on 80,000-node K-Computer

Biwire structure of methanol inside carbon nanotubes

Structure of water confined inside carbon nanotubes and water models

Possibility of Gas Sensor Using Electronic Transport Properties of Iron−Porphyrin Molecular Junction System

Theoretical study on diffusion mechanism of fluorine atom adsorbed on Si(111) reconstructed surface

Lattice parameter dependence of energy barriers of hydrogenation of ultra small carbon nanotubes

Tautomerism in Reduced Pyrazinacenes

Investigation of the Mechanism of Adsorption of β-Nicotinamide Adenine Dinucleotide on Single-Walled Carbon Nanotubes

First-principles supercell calculations for simulating a shallow donor state in Si

Hydrogenation of ultrasmall carbon nanotubes: A first principle study

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