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| 1.
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Oda, Tatsuki ; Sugimori, K. ; Nagao, Hidemi ; Hamada, I. ; Kagayama, S. ; Geshi, M. ; Nagara, H. ; Kusakabe, K. ; Suzuki, N.
概要:
金沢大学大学院自然科学研究科計算科学<br />金沢大学工学部<br />We have studied the ζ-phase of solid oxygen using the generalized gradient approxim
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ation in the density functional approach. Calculations of total energies and pressures have been carried out for the prototype of diatomic ζ-phase and other hypothetical monoatomic crystal structures. The diatomic phase was found to be stable over a wide range of pressure (100-2000GPa). The stacking of molecular layers is discussed in comparison with the available experimental data. © IOP Publishing Ltd.
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| 2.
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Oda, Tatsuki ; Pasquarello, Alfredo ; Car, Roberto
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金沢大学大学院自然科学研究科計算科学<br />金沢大学理学部<br />We develop a plane-wave pseudopotential scheme for noncollinear magnetic structures
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, based on a generalized local spin-density theory in which the direction of the magnetization is a continuous variable of position. We allow the atomic and magnetic structures to relax simultaneously and self-consistently. Application to small Fe clusters yields noncollinear magnetic structures for Fe3 and Fe5. The components of the magnetization density vary smoothly with position. The spin direction undergoes sizable changes only in the regions of small charge and spin density between the atoms and is generally uniform in the magnetic regions of the atoms.
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| 3.
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Oda, Tatsuki ; Pasquarello, Alfredo
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金沢大学大学院自然科学研究科計算科学<br />金沢大学理学部<br />We perform first-principles molecular dynamics of liquid oxygen in which the magnet
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ic structure evolves according to a generalized density-functional scheme allowing for noncollinear spin configurations. We investigate both structural correlations between the orientations of the molecular axes and magnetic correlations between the orientations of the molecular magnetic moments, demonstrating a clear relation between the local molecular configuration and the relative magnetic arrangement. The nuclear structure factor obtained from the simulation is found to agree well with the experimental one. The calculated magnetic structure factor shows antiferromagnetic correlations between molecules in the first shell, in accord with spin-polarized neutron scattering measurements. We observe the formation of dynamically coupled molecules, known as O4 units, in which the molecular moments are aligned in an antiferromagnetic fashion. An analysis based on the life time of such units, revealed that in most cases the O4 units occur as transient configurations during collisions. However, we also observed a small fraction of O4 units surviving for relatively long periods. To account for electronic excitations which are missed in our density-functional scheme, we complement our description with a mean field model for the thermal fluctuations of the magnetic structure. The combined scheme is found to improve the description of the magnetic neutron structure factor and allows us to study the dependence of the magnetic susceptibility on temperature.
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Hosokawa, A. ; Tsujikawa, M. ; Shiroishi, H. ; Oda, Tatsuki
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金沢大学大学院自然科学研究科計算科学<br />金沢大学理学部<br />We have developed a fully relativistic pseudopotential in the planewave method. The
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pseudopotential shows the sufficient transferability that the error is much smaller than the energy splitting of spin-orbit coupling. This pseudopotential scheme has been implemented for bulk systems, surfaces, and the thin magnetic film on the metal. © 2006 Elsevier B.V. All rights reserved.
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| 5.
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Oda, Tatsuki ; Hosokawa, Akihiko
概要:
金沢大学大学院自然科学研究科計算科学<br />金沢大学理学部<br />We have introduced effects of spin-orbit interaction nonperturbatively to the ultra
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soft-pseudopotential scheme accompanied by two component spinor wave functions. Application to the electronic structure calculations of some heavy elements successfully reproduced results of the all electron approaches. The magnetic anisotropy energy and the orbital magnetic moment for alloys, which have shown a good agreement with the previous results, demonstrated broad capabilities of the approach. © 2005 The American Physical Society.
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| 6.
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Shiroishi, H. ; Oda, Tatsuki ; Sakashita, H. ; Fujima, N.
概要:
金沢大学大学院自然科学研究科計算科学<br />金沢大学理学部<br />We have studied the electronic structure of the carbon nanotubes which include Fe a
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tomic wire with using the density functional theory. As the stable geometries, we obtained the straight and zigzag wires, which have ferromagnetic and antiferromagnetic alignments, respectively. The antiferromagnets consists of the two ferromagnetic dimers which couple in antiparallel alignment. We presents the band dispersions and the density of states for the magnetic nanotubes. The electronic structure at the Fermi level consists of the Fe 3d and C 2pπ states, which shows a strong hybridization between them. © EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2007.
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| 7.
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Oda, Tatsuki ; Pasquarello, Alfredo
概要:
金沢大学大学院自然科学研究科計算科学<br />金沢大学理学部<br />The ab initio molecular dynamics was performed toinvestigate the noncollinear magne
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tism of a system with an evolving atomic structure. As such, application to liquid oxygen provides a picture in which the large majority of colliding O2 molecules assume structural and magnetic configurations which closely resemble those in the O4 molecule. Formation of truly long-living molecular O4 units also occurs but involves a considerably smaller fraction of O2 molecules.
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| 8.
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Tsujikawa, Masahito ; Hosokawa, Akihiko ; Oda, Tatsuki
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金沢大学理工研究域 数物科学系<br />We investigated the magnetic anisotropy of an iron layer on a Pt(001) surface and some related syst
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ems by employing the local spin density approximation in a theoretical ab initio approach. We found that the surface system Pt/Fe/Pt (001) showed a perpendicular magnetic anisotropy and its anisotropy energy per iron atom amounted to a value which is 2 times larger than the value of bulk FePt. The surface relaxation much enhances the anisotropy energies, related to a large attractive force between the iron and platinum layers. A remarkable cap effect-that the covering platinum layer changes anisotropy energy-was also found to exist. We investigated the microscopic origin of the perpendicular anisotropy in relation to the local densities of states of the Fe atom. These quantities were discussed as a fingerprint of magnetic anisotropy in comparison with the results of the Fe chain at the step edge on a vicinal surface Pt(664). The atomic orbital magnetic moments were enhanced at the respective surface atoms. © 2008 The American Physical Society.
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| 9.
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Obata, Masao ; Hamada, Ikutaro ; Oda, Tatsuki
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We introduce scaling parameters for the spin-polarization dependent gradient correction to the local correlation in the
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van der Waals density functional, which enable us to tune the magnetic interaction between atoms and molecules. We have applied the method to solid oxygen and found that by using an optimal choice of the parameters, the structural parameters are significantly improved over the ones obtained in the previous work. We discuss the generic features of the proposed approach. © 2015 The Authors. Published by Elsevier B.V.<br />20th International Conference on Magnetism, ICM 2015; Palau de Congressos de Catalunya679, Avinguda DiagonalBarcelona; Spain; 5 July 2015 through 10 July 2015
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| 10.
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Oda, Tatsuki ; Okada, Isamu ; Kojima, Kenichi ; Wako, Kei ; Tachibana, Masaru
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金沢大学理工研究域 数物科学系<br />Simulations of double-walled carbon nanotubes under bending deformation using the tight-binding mol
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ecular dynamics method were carried out. Five- and seven-membered ring pair defects were formed after emission of several atoms from the tube structure. These defect pair couples have different structures corresponding to the number of emitted atoms and stabilize the resulting nanotubes. Our results imply that the defect pair couples represent one of the potential origins of the experimentally observed plastic deformations that have been shown to occur in double-walled carbon nanotubes. The various defects obtained by the simulations are discussed in relation to other defect types. © 2007 American Institute of Physics.
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