- 著者
- Okada Susumu Saito Susumu Oshiyama Atsushi
- 出版者
- American Physical Society
- 雑誌
- Physical review B (ISSN:10980121)
- 巻号頁・発行日
- vol.64, no.20, pp.201303, 2001-10
- 被引用文献数
- 33 39
We report first-principles total-energy electronic-structure calculations that provide energetics of encapsulation of C60 in nanotubes consisting of boron and nitrogen atoms and electronic structures of resulting “BNC peapods.” We find that the encapsulating process is exothermic for (10,10) and (9,9) nanotubes. The energy gain upon the encapsulation is larger than that for carbon peapods, so that the BN nanotube is a promising candidate to accommodate the fullerenes inside. The material is predicted to be a new form of ternary semiconductor with interesting structural hierarchy.
- 著者
- Okada Susumu Saito Susumu Oshiyama Atsushi
- 出版者
- American Physical Society
- 雑誌
- Physical review B (ISSN:10980121)
- 巻号頁・発行日
- vol.65, no.16, pp.165410, 2002-04
- 被引用文献数
- 74 83
We report first-principles total-energy electronic-structure calculations that provide energetics and electronic structures of double-walled BN nanotubes, (n,0)@(15,0) and (m,0)@(20,0). We find that the most favorable double-walled nanotubes studied here are (7,0)@(15,0) and (12,0)@(20,0) in which the interwall distances are about 3 Å. The electronic energy bands around the Fermi energy depend interestingly on the tube radii due to the hybridization between σ and π states. We also find that the nearly-free-electron states of the nanotubes induce peculiar charge redistribution in the interwall region.
- 著者
- Okada Susumu Oshiyama Atsushi
- 出版者
- American Physical Society
- 雑誌
- Physical review B (ISSN:10980121)
- 巻号頁・発行日
- vol.68, no.23, pp.235402, 2003-12
- 被引用文献数
- 26
We report electronic structures and stabilities of rhombohedral C60 polymers by using the local spin-density approximation in the framework of the density-functional theory. Owing to hybrid networks of sp2-like (threefold coordinated) and sp3-like (fourfold coordinated) carbon atoms, the electronic structures of these polymers are considerably different from that of a face-centered cubic (fcc) C60. We find that polymerized structures attained at the double bonds are semiconducting whereas polymerized structures attained at single bonds are metallic. Significant overlap of the wave function in the space among three adjacent C60 causes the metallic behavior on the latter polymers. We also find that the stacking ordering strongly affects the conducting properties of the metallic polymers. Despite substantial density of states at Fermi level, the C60 polymers do not exhibit any magnetic ordering. Total energy calculations show that the metallic C60 polymers have higher total energy than the semiconducting C60 polymer phases.
- 著者
- Okada Susumu Otani Minoru Oshiyama Atsushi
- 出版者
- American Physical Society
- 雑誌
- Physical review B (ISSN:10980121)
- 巻号頁・発行日
- vol.67, no.20, pp.205411, 2003-05
- 被引用文献数
- 96 93
We report total-energy electronic structure calculations that provide energetics of encapsulation of various fullerenes in carbon nanotubes and electronic structures of resulting carbon peapods. We find that the electron states of the peapods depend on the space in the nanotubes and that they reflect electron states of the encapsulated fullerenes. The deep energy position of the lowest unoccupied state of fullerenes as well as hybridization between π states of the fullerenes and the nearly free-electron states of the nanotubes causes a multicarrier character in the peapods.
- 著者
- Okada Susumu Oshiyama Atsushi
- 出版者
- American Physical Society
- 雑誌
- Physical review letters (ISSN:00319007)
- 巻号頁・発行日
- vol.87, no.14, pp.146803, 2001-09
- 被引用文献数
- 333
We report first-principles total-energy electronic-structure calculations in the density-functional theory performed for hexagonally bonded honeycomb sheets consisting of B, N, and C atoms. We find that the ground state of BNC sheets with particular stoichiometry is ferromagnetic. Detailed analyses of energy bands and spin densities unequivocally reveal the nature of the ferromagnetic ordering, leading to an argument that the BNC sheet is a manifestation of the flat-band ferromagnetism.
- 著者
- Okada Susumu Shiraishi Kenji Oshiyama Atsushi
- 出版者
- American Physical Society
- 雑誌
- Physical review letters (ISSN:00319007)
- 巻号頁・発行日
- vol.90, no.2, pp.026803, 2003-01
- 被引用文献数
- 33 21
Based on total-energy electronic-structure calculations within the density-functional theory, we find that a high spin state is realized for an ultimate dangling bond unit on an otherwise hydrogen-covered Si(111) surface. We further propose a systematic method of constructing nanometer-scale dangling bond networks that exhibit the ferrimagnetic spin ordering. The interplay between the electron-electron interaction and the surface reconstruction is elucidated.
- 著者
- Okada Susumu Oshiyama Atsushi
- 出版者
- American Physical Society
- 雑誌
- Physical review letters (ISSN:00319007)
- 巻号頁・発行日
- vol.91, no.21, pp.216801, 2003-11
- 被引用文献数
- 73 70
We report total-energy electronic-structure calculations that provide energetics and electronic structures of double-walled carbon nanotubes consisting of semiconducting (n,0) nanotubes. We find that optimum spacing between the walls of the nanotubes is slightly larger than the interlayer spacing of the graphite. We also find that the electronic structures of the double-walled nanotubes with the inner (7,0) nanotube are metallic with multicarrier characters in which electrons and holes exist on inner and outer nanotubes, respectively. Interwall spacing and curvature difference are found to be essential for the electron states around the Fermi level.
- 著者
- Boero Mauro Oshiyama Atsushi Silvestrelli Pier Luigi
- 出版者
- American Physical Society
- 雑誌
- Physical review letters (ISSN:00319007)
- 巻号頁・発行日
- vol.91, no.20, pp.206401, 2003-11
- 被引用文献数
- 27 22
The displacement of an oxygen atom in pure α quartz is studied via first-principles molecular dynamics. The simulations show that when an O atom in a Si-O-Si bridge is moved away from its original equilibrium position, a new stable energy minimum can be reached. Depending on the spin state and charge Q of the system, this minimum can give rise to either a threefold oxygen (singlet ground state and Q=+1) or to an unsaturated Si atom carrying a dangling bond (triplet state). In the latter case, the hyperfine parameters associated with the 29Si dangling bond are in rather good agreement with electron paramagnetic resonance/electron nuclear double resonance experiments.
- 著者
- Okada Susumu Oshiyama Atsushi
- 出版者
- American Physical Society
- 雑誌
- Physical review letters (ISSN:00319007)
- 巻号頁・発行日
- vol.95, no.20, pp.206804, 2005-11
- 被引用文献数
- 45 43
A total-energy electronic-structure calculation is performed to explore energetics and electronic structures of nanotubes adsorbed on metal surfaces. We find that the charge transfer from metal surfaces to the nanotubes takes place depending on both the electronic structures of the adsorbed nanotubes and the work functions of the metal surfaces. In addition, we also find a substantial hybridization between the electron states of metal atoms and those of the nanotubes, which results in the metal-induced inhomogeneous charge distribution in the nanotubes.
- 著者
- Boero Mauro Oshiyama Atsushi Silvestrelli Pier Luigi Murakami Kouichi
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.86, no.20, pp.201910, 2005-05
- 被引用文献数
- 17 18
Recent experiments have shown that pure Si structures in a matrix of SiO2 can be formed by electron excitation techniques, with appealing applications in nanotechnology. Our ab initio simulations provide an insight into the underlying mechanism, showing that electron excitations weaken Si–O bonds in SiO2, dislodge O atoms and allow Si dangling bonds to reconstruct in stable Si–Si structures below the melting temperature. Differences in diffusivity of O (fast) and Si (slow) are shown to play a decisive role in the process.
- 著者
- Boero Mauro Oshiyama Atsushi Silvestrelli Pier Luigi Murakami Kouichi
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.86, pp.201910, 2005-05
- 被引用文献数
- 17
Recent experiments have shown that pure Si structures in a matrix of SiO2 can be formed by electron excitation techniques, with appealing applications in nanotechnology. Our ab initio simulations provide an insight into the underlying mechanism, showing that electron excitations weaken Si–O bonds in SiO2, dislodge O atoms and allow Si dangling bonds to reconstruct in stable Si–Si structures below the melting temperature. Differences in diffusivity of O (fast) and Si (slow) are shown to play a decisive role in the process.