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Journal Articles

Nuclear quantum effects of light and heavy water studied by all-electron first principles path integral simulations

Machida, Masahiko; Kato, Koichiro*; Shiga, Motoyuki

Journal of Chemical Physics, 148(10), p.102324_1 - 102324_11, 2018/03

AA2017-0553.pdf:4.95MB

 Times Cited Count:5 Percentile:10.33(Chemistry, Physical)

The isotopologs of liquid water, H$$_{2}$$O, D$$_{2}$$O, and T$$_{2}$$O, are studied systematically by first principles PIMD simulations, in which the whole entity of the electrons and nuclei are treated quantum mechanically. The simulation results are in reasonable agreement with available experimental data on isotope effects, in particular, on the peak shift in the radial distributions of H$$_{2}$$O and D$$_{2}$$O and the shift in the evaporation energies. It is found that, due to differences in nuclear quantum effects, the H atoms in the OH bonds more easily access the dissociative region up to the hydrogen bond center than the D (T) atoms in the OD (OT) bonds. The accuracy and limitation in the use of the current density-functional-theory-based first principles PIMD simulations are also discussed. It is argued that the inclusion of the dispersion correction or relevant improvements in the density functionals are required for the quantitative estimation of isotope effects.

Journal Articles

Atomistic and continuum comparative studies on the stress distribution around a nano-crack on the grain boundary for modeling hydrogen embrittlement of iron

Ebihara, Kenichi; Kaburaki, Hideo; Itakura, Mitsuhiro

"Hagane No Kikaiteki Tokusei Ni Oyobosu Suiso No Koka To Sono Hyoka" Shimpojium Yokoshu (USB Flash Drive), 6 Pages, 2014/09

Since hydrogen(H) embrittlement is one factor causing degradation and/or fracture of steel, understanding its mechanism is required. The grain-boundary(GB) decohesion due to segregation of H is considered to cause the delayed fracture of high strength steels and the cold cracking in welding. In the model based on GB decohesion, information of strength of GBs estimated in the atomic scale is used for the estimation of strength or crack propagation in the macroscopic scale. However the modeling between the atomic and the macroscopic scales is not clear. In particular, the validity of the model using the elastic continuum around nano-cracks for stress concentration at the crack tip is not clear. Thus, we examined the difference of the stress distribution around the nano-crack which was estimated by molecular dynamics and by a continuum calculation. As a result, the discrepancy became remarkable at high strain. The stress concentration was not simulated by the elastic continuum model.

Journal Articles

Structural study of molten lanthanum halides by X-ray diffraction and computer simulation techniques

Okamoto, Yoshihiro; Madden, P. A.*

Journal of Physics and Chemistry of Solids, 66(1), p.448 - 451, 2005/01

The local structure of molten LaCl$$_3$$ has been characterized by the octahedral coordination (LaCl$$_6$$)$$^{3-}$$. It is based on X-ray diffraction (XRD) and Raman spectroscopy results. On the other hand, a different structural image was proposed in the neutron diffraction (ND) and the molecular dynamics (MD) studies. These ND and MD works concluded that a coordination behavior changes with cation size in molten rare earth trichlorides. Thus, they reported the coordination number of Cl$$^-$$ ions around La$$^{3+}$$ ion is 8.2 in the ND work and 7.9 in the MD work. In the present work, XRD measurements of molten LaCl$$_3$$ were performed to investigate the local structure. The coordination number of the 1st La$$^{3+}$$-Cl$$^-$$ pair in molten LaCl$$_3$$ was 7.1 from analysis of the correlation function G(r). The structural change by increasing anion size was examined by the XRD measurement of molten LaBr$$_3$$. The XRD data were nicely reproduced by the MD simulations with polarizable ionic model.

Journal Articles

XAFS simulation of highly disordered materials

Okamoto, Yoshihiro

Nuclear Instruments and Methods in Physics Research A, 526(3), p.572 - 583, 2004/07

 Times Cited Count:25 Percentile:13.7(Instruments & Instrumentation)

The XAFS functions for highly-disordered materials such as molten salts were simulated by using output data of molecular dynamics calculation. The atomic configuration data obtained from the MD results was directly used as input data in the XAFS simulation code FEFF8. It was assumed that Debye-Waller factor and anharmonic vibration effect could be substituted by an accumulation of the FEFF8 calculations using many atomic configurations. The experimental XAFS functions for platinum, solid and molten salt systems were nicely reproduced by the FEFF8 calculations with 10000-50000 atomic configurations.

Journal Articles

Quantum path-integral molecular dynamics calculations of the dipole-bound state of the water dimer anion

Shiga, Motoyuki; Takayanagi, Toshiyuki

Chemical Physics Letters, 378(5-6), p.539 - 547, 2003/09

 Times Cited Count:7 Percentile:75.64

no abstracts in English

Journal Articles

X-ray absorption study of molten uranium chloride system

Okamoto, Yoshihiro; Akabori, Mitsuo; Ito, Akinori; Ogawa, Toru

Journal of Nuclear Science and Technology, 39(Suppl.3), p.638 - 641, 2002/11

We report local structural features of molten UCl$$_3$$ with LiCl-KCl eutectic probed by the U L$$_3$$-edge XAFS(X-ray absorption fine structure). The XAFS measurements were performed in a transmission mode at the BL27B station of the Photon Factory(High Energy Accelerator Organization, Tsukuba, JAPAN). Sample prepared by chlorination of uranium hydride and then reduction with zinc powder was sealed in a quartz cell under reduced pressure. The nearest U$$^{3+}$$-Cl$$^-$$ distance and the coordination number of Cl$$^-$$ around U$$^{3+}$$ ion were obtained by a curve fitting of the 1st shell XAFS function k$$^3$$$$chi$$(k). The pair potential in the U$$^{3+}$$-Cl$$^-$$ correlation was evaluated from XAFS simulation by combinational use of the MD and the FEFF8. In addition, valence state of uranium in the melt was evaluated by XANES(X-ray absorption near edge structure) spectra.

Journal Articles

XAFS study of molten zinc dibromide

Okamoto, Yoshihiro; Fukushima, Kazuko*; Iwadate, Yasuhiko*

Journal of Non-Crystalline Solids, 312(314), p.450 - 453, 2002/10

Local structure of molten ZnBr$$_2$$ was investigated by both of the Zn and the Br XAFS(X-ray absorption fine structure) measurements above their K-absorption edge at 723K. The nearest Zn$$^{2+}$$-Br$$^-$$ distance was determined to be 2.46$AA  for the Zn XAFS and 2.45AA for the Br XAFS.  The coordination number of Br$^-$$ ion around Zn$$^{2+}$$ was about 4. On the other hand, that of Zn$$^{2+}$$ ion around Br$$^-$$ was about 2. The 1st Br$$^-$$-Br$$^-$$ distance was estimated to be 3.9$AA.  They shows that a tetrahedral coordinate (ZnBr$_4$$)$$^{2-}$$ exists and most of the coordinate connects with the next ones through Br$$^-$$ ion. The two XAFS functions in the molten ZnBr$$_2$$ were reproduced by the combination of the molecular dynamics(MD) simulation and the FEFF7 computations.

Journal Articles

Development of parallel molecular-dynamics simulation stencil

Shimizu, Futoshi; Kimizuka, Hajime*; Kaburaki, Hideo; Arakawa, Chuichi*

Keisan Kogaku Koenkai Rombunshu, 7(1), p.163 - 166, 2002/05

no abstracts in English

Journal Articles

Development of parallel molecular dynamics stencil

Shimizu, Futoshi; Kimizuka, Hajime*; Kaburaki, Hideo; Arakawa, Chuichi*

Nippon Keisan Kogakkai Rombunshu, 4, p.225 - 230, 2002/04

no abstracts in English

Journal Articles

High speed calculation for solid molecular dynamics on vector processors

Itakura, Kenichi; Yokokawa, Mitsuo; Shimizu, Futoshi; Kimizuka, Hajime*; Kaburaki, Hideo

Joho Shori Gakkai Kenkyu Hokoku 2001-HPC-88, p.67 - 72, 2001/10

he Earth Simulator which is under development has 640 processor nodes and its peak performance is 40 Tflop/s. In this study, we have evaluated performance of solid molecular dynamics simulation on an SMP node of the Earth Simulator. In molecular dynamics simulation, each particle is influenced by all particles within a cut-off region and the representation of these pairs of particles is made by a matrix. Two matrix representations, compressed row form and jagged diagonal form, are considered for vectorization. The jagged diagonal form is better than the compressed row form in performance on a vector processor for the force calculation of every pairs, because the vector length of the former is longer than that of the latter. However, computational cost for converting the normal matrix form to the jagged diagonal form is quite expensive and the total performance in using the jagged diagonal form is low. Speedup by parallelization with the compressed row form is 2.4 to 2.7 with 8 vector processors.

Journal Articles

Molecular dynamics analysis of laser shock phenomena due to Gaussian beam irradiation

Fukumoto, Ichiro; Omura, Etsuji*

Seimitsu Kogakkai-Shi, 67(6), p.916 - 921, 2001/06

no abstracts in English

Journal Articles

Zirconium microclusters; Molecular-dynamics simulations and density functional calculations

Bastug, T.*; Erkoc, S.*; Hirata, Masaru; Tachimori, Shoichi

Physica E, 8(3), p.223 - 229, 2000/09

 Times Cited Count:4 Percentile:69.62

no abstracts in English

Journal Articles

Parrallel molecular dynamics simulation on elastic properties of solid argon

Shimizu, Futoshi; Kimizuka, Hajime*; Kaburaki, Hideo; Li, J.*; Yip, S.*

Proceedings of 4th International Conference on Supercomputing in Nuclear Applications (SNA 2000) (CD-ROM), 10 Pages, 2000/09

no abstracts in English

Journal Articles

Mechanism for negative poisson ratios over the $$alpha$$-$$beta$$ transition of cristobalite, SiO$$_{2}$$; A Molecular-dynamics study

Kimizuka, Hajime*; Kaburaki, Hideo; Kogure, Yoshiaki*

Physical Review Letters, 84(24), p.5548 - 5551, 2000/06

 Times Cited Count:90 Percentile:7.92(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Molecular dynamics analysis of negative poisson ratios over the $$alpha$$-$$beta$$ transition in cristobalite, SiO$$_{2}$$

Kimizuka, Hajime*; Kaburaki, Hideo; Shimizu, Futoshi; Kogure, Yoshiaki*

Progress of Theoretical Physics Supplement, (138), p.229 - 233, 2000/04

no abstracts in English

JAEA Reports

None

Yamanaka, Shinsuke*; Abe, Kazuyuki

JNC-TY9400 2000-004, 78 Pages, 2000/03

JNC-TY9400-2000-004.pdf:2.39MB

no abstracts in English

JAEA Reports

Parallelization for first principles molecular dynamics programs

Watabe, Hiroshi*; Kobayashi, Kazuaki*; Arai, Masao*

JAERI-Data/Code 2000-019, p.33 - 0, 2000/03

JAERI-Data-Code-2000-019.pdf:1.54MB

no abstracts in English

Journal Articles

The Reverse Monte Carlo studies of molten alkali carbonates

Kohara, Shinji*; Suzuya, Kentaro; Ono, Hideo

Proceedings of 12th International Symposium on Molten Salts (Molten Salts 12), 99-41, p.253 - 262, 1999/10

no abstracts in English

Journal Articles

Particle simulation for heat and fluid flow

Watanabe, Tadashi

Dennetsu, 38(149), p.8 - 13, 1999/03

no abstracts in English

Journal Articles

Chain structure of liquid and amorphous selenium: tight-binding molecular-dynamics simulation

; Kaburaki, Hideo; *; *

Journal of Non-Crystalline Solids, 250-252(2), p.433 - 436, 1999/00

no abstracts in English

39 (Records 1-20 displayed on this page)