CMSセミナー2010
GPU Utilization Method and GPU Acceleration of Diffusion Monte Carlo Method
GPUの利用方法とGPUによる拡散モンテカルロ法の高速化
Mr. Teppei Ono (小野哲平氏)
【Date & Time】30 November 2010 (Tue), 16:00 -- 17:00
【Place】4F seminar room (#431-2), MANA Bldg., Namiki site (並木地区MANA棟4Fセミナー室)
【Speaker】Mr. Teppei Ono (小野哲平氏)
【Affiliation】SQUARE ENIX CO., LTD. (株式会社スクウェア・エニックス)
【Title】GPU Utilization Method and GPU Acceleration of Diffusion Monte Carlo Method
GPUの利用方法とGPUによる拡散モンテカルロ法の高速化
【Abstract】
近年、グラフィックスプロセッサーユニット（GPU）は目覚しい性能の向上を遂げ、新たな計算資源として計算科学の分野に利用することが重要視されている。課題とされていた計算精度の問題は倍精度演算可能なGPUが登場することによって解消され、電子状態計算の分野での利用が現実的となった。GPUに限らず、今後は何らかのアクセラレータを用いた数値計算が主流になることが十分予想される。我々はそれぞれのアーキテクチャの特性を理解した上で、適切な利用手段を選択しなければならない。本講演ではGPUを科学計算に使うための手順、並列化手段、最適化方法を解説し、GPUを第一原理計算に利用した例として拡散モンテカルロ法をGPUを用いて計算した例を紹介する。また、今後の新アーキテクチャへの対応を視野に入れた柔軟なソースコード記述方法の一例を提案する。
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】4F seminar room (#431-2), MANA Bldg., Namiki site (並木地区MANA棟4Fセミナー室)
【Speaker】Mr. Teppei Ono (小野哲平氏)
【Affiliation】SQUARE ENIX CO., LTD. (株式会社スクウェア・エニックス)
【Title】GPU Utilization Method and GPU Acceleration of Diffusion Monte Carlo Method
GPUの利用方法とGPUによる拡散モンテカルロ法の高速化
【Abstract】
近年、グラフィックスプロセッサーユニット（GPU）は目覚しい性能の向上を遂げ、新たな計算資源として計算科学の分野に利用することが重要視されている。課題とされていた計算精度の問題は倍精度演算可能なGPUが登場することによって解消され、電子状態計算の分野での利用が現実的となった。GPUに限らず、今後は何らかのアクセラレータを用いた数値計算が主流になることが十分予想される。我々はそれぞれのアーキテクチャの特性を理解した上で、適切な利用手段を選択しなければならない。本講演ではGPUを科学計算に使うための手順、並列化手段、最適化方法を解説し、GPUを第一原理計算に利用した例として拡散モンテカルロ法をGPUを用いて計算した例を紹介する。また、今後の新アーキテクチャへの対応を視野に入れた柔軟なソースコード記述方法の一例を提案する。
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Spin spirals in underdoped cuprates: theory and experiment
Prof. Oleg Sushkov
【Date & Time】24 November 2010 (Wed), 11:00 am -
【Place】8F seminar room, Central Bldg., Sengen site
【Speaker】Prof. Oleg Sushkov
【Affiliation】School of Physics, The University of New South Wales, Sydney
【Title】Spin spirals in underdoped cuprates: theory and experiment
【Abstract】
To shed light on generic physics of cuprate superconductors (doped Mott insulators) I discuss and relate the following issues.
1)Incommensurate spin ordering in LSCO and YBCO.
2)Difference and similarities between these compounds : disorder versus bilayer.
3)Quantum Critical and Lifshitz points in YBCO and LSCO.
4)Magnetic Quantum Oscillations in YBCO.
5)Recent MSR data.
【Contact】Dr. Hiroyuki Yamase(山瀬博之)
【Place】8F seminar room, Central Bldg., Sengen site
【Speaker】Prof. Oleg Sushkov
【Affiliation】School of Physics, The University of New South Wales, Sydney
【Title】Spin spirals in underdoped cuprates: theory and experiment
【Abstract】
To shed light on generic physics of cuprate superconductors (doped Mott insulators) I discuss and relate the following issues.
1)Incommensurate spin ordering in LSCO and YBCO.
2)Difference and similarities between these compounds : disorder versus bilayer.
3)Quantum Critical and Lifshitz points in YBCO and LSCO.
4)Magnetic Quantum Oscillations in YBCO.
5)Recent MSR data.
【Contact】Dr. Hiroyuki Yamase(山瀬博之)
Theory of multi-electron transfer reactions:implications for electrocatalysis
Prof. Marc T. M. Koper
【Date & Time】2 August 2010 (Mon) 16:00 - 17:00
【Place】4F seminar room (#409-10), Collaborative Research Bldg., Namiki site /並木地区共同研究棟4Fゼミナール室
【Speaker】Prof. Marc T. M. Koper
【Affiliation】Leiden Institute of Chemistry, Leiden University
【Title】Theory of multi-electron transfer reactions:implications for electrocatalysis
【Abstract】
Practically all relevant electrocatalytic reactions require the transfer of at least two electrons, and often more than two. A full theory of such reactions does not only require knowledge of the activation energy associated with the event of a single electron, i.e. Marcus theory and its various extensions, but also insight into the relative energies of the intermediate states, i.e. the thermodynamics of all intermediates and the associated elementary steps in which they are formed. Based on this idea, I will show that are fundamental differences in the catalysis of reactions involving 1, 2 or more than 2 electrons, or, partly equivalently, reactions involving 0, 1, or 2 or more catalytic intermediates. For the latter two classes, knowing the thermodynamics of the full reaction is more important than the ability to predict the activation energy of a single step, and in fact the optimal catalyst is first and foremost that material that is able to generate a “thermodynamic landscape” that does not have a sink or mountain. In essence, this is a multidimensional Sabatier principle for the optimal catalyst. The principle will be illustrated on a few examples of important electrocatalytic reactions.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】4F seminar room (#409-10), Collaborative Research Bldg., Namiki site /並木地区共同研究棟4Fゼミナール室
【Speaker】Prof. Marc T. M. Koper
【Affiliation】Leiden Institute of Chemistry, Leiden University
【Title】Theory of multi-electron transfer reactions:implications for electrocatalysis
【Abstract】
Practically all relevant electrocatalytic reactions require the transfer of at least two electrons, and often more than two. A full theory of such reactions does not only require knowledge of the activation energy associated with the event of a single electron, i.e. Marcus theory and its various extensions, but also insight into the relative energies of the intermediate states, i.e. the thermodynamics of all intermediates and the associated elementary steps in which they are formed. Based on this idea, I will show that are fundamental differences in the catalysis of reactions involving 1, 2 or more than 2 electrons, or, partly equivalently, reactions involving 0, 1, or 2 or more catalytic intermediates. For the latter two classes, knowing the thermodynamics of the full reaction is more important than the ability to predict the activation energy of a single step, and in fact the optimal catalyst is first and foremost that material that is able to generate a “thermodynamic landscape” that does not have a sink or mountain. In essence, this is a multidimensional Sabatier principle for the optimal catalyst. The principle will be illustrated on a few examples of important electrocatalytic reactions.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Recent developments in theory of superfluidity
Prof. Yusuke Kato
【Date & Time】06 July 2010 (Tue), 15:30 -
【Place】8F large seminar room, Sengen site/千現地区８階中セミナー室
【Speaker】Professor Yusuke Kato
【Affiliation】Department of Basic Science, The University of Tokyo
【Title】Recent developments in theory of superfluidity
【Abstract】
We discuss recent developments in the theory of superfluidity in condensed Bose-Einstein systems, with a particular focus on a stability criterion of a superfluid phase. We showed in [1,2] that dynamical density fluctuations of superfluids are enhanced near the critical velocity in two kinds of instability: in the Landau instability and in the soliton emission instability . On the basis of this finding, we propose a new criterion for stability of superfluid.
References:
[1] Y. Kato and S. Watabe, J. Low Temp. Phys. 158, 92 (2010) "Generalized Criterion for Stability of Superflow Past an Obstacle"
[2] Y. Kato and S. Watabe, arXiv:1006.2999 (2010) "Dynamical density fluctuations of superfluids near the critical velocity"; PRL, to appear.
【Contact】Dr. Akihiro Tanaka(田中秋広）
【Place】8F large seminar room, Sengen site/千現地区８階中セミナー室
【Speaker】Professor Yusuke Kato
【Affiliation】Department of Basic Science, The University of Tokyo
【Title】Recent developments in theory of superfluidity
【Abstract】
We discuss recent developments in the theory of superfluidity in condensed Bose-Einstein systems, with a particular focus on a stability criterion of a superfluid phase. We showed in [1,2] that dynamical density fluctuations of superfluids are enhanced near the critical velocity in two kinds of instability: in the Landau instability and in the soliton emission instability . On the basis of this finding, we propose a new criterion for stability of superfluid.
References:
[1] Y. Kato and S. Watabe, J. Low Temp. Phys. 158, 92 (2010) "Generalized Criterion for Stability of Superflow Past an Obstacle"
[2] Y. Kato and S. Watabe, arXiv:1006.2999 (2010) "Dynamical density fluctuations of superfluids near the critical velocity"; PRL, to appear.
【Contact】Dr. Akihiro Tanaka(田中秋広）
Electronic and optical properties of polycrystalline metal-oxide materials
Dr. Keith McKenna
【Date & Time】01 July 2010 (Thu) 16:00 - 17:00
【Place】8F large seminar room, Sengen site/千現地区８F中セミナー室
Speaker】Dr. Keith McKenna
【Affiliation】CMMP, University College London & WPI-AIMR, Tohoku University
【Title】Electronic and optical properties of polycrystalline metal-oxide materials
【Abstract】
Although polycrystalline metal-oxide materials and nanopowders are ubiquitous in nature, and find numerous technological applications, surprisingly little is known about their electronic properties.
In this talk, I will present recent results on the electronic properties of metal-oxide interfaces and surfaces that have been obtained by quantum-mechanical calculations. These will include studies of optical excitation and charge trapping in MgO nanopowders, and defect segregation and electron trapping at grain boundaries in MgO and HfO2. The implications of the results for technological applications such as solid oxide fuel cells, catalysts and MOSFETs will be discussed.
References:
K. McKenna et al, APL 95, 222111 (2009)
PRB 79, 224116 (2009); Micro. Eng. 86, 1751-1755 (2009)
Nature Materials 7, 859-862 (2008); JACS 129, 8600-8608 (2007)
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】8F large seminar room, Sengen site/千現地区８F中セミナー室
Speaker】Dr. Keith McKenna
【Affiliation】CMMP, University College London & WPI-AIMR, Tohoku University
【Title】Electronic and optical properties of polycrystalline metal-oxide materials
【Abstract】
Although polycrystalline metal-oxide materials and nanopowders are ubiquitous in nature, and find numerous technological applications, surprisingly little is known about their electronic properties.
In this talk, I will present recent results on the electronic properties of metal-oxide interfaces and surfaces that have been obtained by quantum-mechanical calculations. These will include studies of optical excitation and charge trapping in MgO nanopowders, and defect segregation and electron trapping at grain boundaries in MgO and HfO2. The implications of the results for technological applications such as solid oxide fuel cells, catalysts and MOSFETs will be discussed.
References:
K. McKenna et al, APL 95, 222111 (2009)
PRB 79, 224116 (2009); Micro. Eng. 86, 1751-1755 (2009)
Nature Materials 7, 859-862 (2008); JACS 129, 8600-8608 (2007)
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Microscopic Theory of Generation and Detection of Spin Current
スピン流はどこまで制御できているのか? — スピン流制御の微視的理論
Prof. Gen Tatara/多々良源准教授
【Date & Time】28 June 2010 (Mon), 14:00 - 15:30
【Place】8F large seminar room, Sengen site/千現地区８階中セミナー室
【Speaker】Prof. Gen Tatara/多々良源准教授
【Affiliation】Department of Physics, Tokyo Metropolitan Univ./首都大学東京 大学院理工学研究科
【Title】Microscopic Theory of Generation and Detection of Spin Current
スピン流はどこまで制御できているのか? — スピン流制御の微視的理論
【Abstract】
近年スピンの流れ（スピン流)の物理が、そのデバイス応用（スピントロニクス）の観点から注目され、盛んに研究されている。スピン流の応用のためには、スピン流の生成と輸送、また既存のエレクトロニクスとの接点に不可欠な電流ースピン流変換を確立することが必要である。現状では、既にそれら全てに多くの興味深い提案がされており、実験的にはスピン流制御は確立してきている。例えば、強磁性金属では電流には必然的にスピン流が伴うし、非磁性体では電場とスピン軌道相互作用を用いたスピンHall効果を用いることでスピン流は生成できる。また、磁化の運動はスピン流の生成も伴うことが知られており、これを用いると強磁性体と非磁性体の接合で、非磁性体内にスピン流を注入することが可能である(スピンポンピング)。最近では円偏向の光を用いたり、温度勾配を用いたスピン流生成(スピンSeebeck効果)も実現されている。スピン流－電流変換はスピン軌道相互作用を用いて可能であることも確認され、この逆スピンHall効果はスピン流の検出に盛んに用いられている。
講演では、こうした現象の理論的理解がどこまで進んでいるかを紹介し、スピン流制御における課題などを議論する。
参考文献
[1] Diffusive versus local spin currents in dynamic spin pumping systems, Akihito Takeuchi, Kazuhiro Hosono, and Gen Tatara, Phys. Rev. B 81, 144405 (2010) .
[2] Perturbation Theory of the Dynamic Inverse Spin Hall Effect with Charge Conservation, Kazuhiro Hosono, Akihito Takeuchi, and Gen Tatara, J. Phys. Soc. Jpn. 79, 014708 (2010) .
【Contact】Dr. Hiori Kino(木野日織）
【Place】8F large seminar room, Sengen site/千現地区８階中セミナー室
【Speaker】Prof. Gen Tatara/多々良源准教授
【Affiliation】Department of Physics, Tokyo Metropolitan Univ./首都大学東京 大学院理工学研究科
【Title】Microscopic Theory of Generation and Detection of Spin Current
スピン流はどこまで制御できているのか? — スピン流制御の微視的理論
【Abstract】
近年スピンの流れ（スピン流)の物理が、そのデバイス応用（スピントロニクス）の観点から注目され、盛んに研究されている。スピン流の応用のためには、スピン流の生成と輸送、また既存のエレクトロニクスとの接点に不可欠な電流ースピン流変換を確立することが必要である。現状では、既にそれら全てに多くの興味深い提案がされており、実験的にはスピン流制御は確立してきている。例えば、強磁性金属では電流には必然的にスピン流が伴うし、非磁性体では電場とスピン軌道相互作用を用いたスピンHall効果を用いることでスピン流は生成できる。また、磁化の運動はスピン流の生成も伴うことが知られており、これを用いると強磁性体と非磁性体の接合で、非磁性体内にスピン流を注入することが可能である(スピンポンピング)。最近では円偏向の光を用いたり、温度勾配を用いたスピン流生成(スピンSeebeck効果)も実現されている。スピン流－電流変換はスピン軌道相互作用を用いて可能であることも確認され、この逆スピンHall効果はスピン流の検出に盛んに用いられている。
講演では、こうした現象の理論的理解がどこまで進んでいるかを紹介し、スピン流制御における課題などを議論する。
参考文献
[1] Diffusive versus local spin currents in dynamic spin pumping systems, Akihito Takeuchi, Kazuhiro Hosono, and Gen Tatara, Phys. Rev. B 81, 144405 (2010) .
[2] Perturbation Theory of the Dynamic Inverse Spin Hall Effect with Charge Conservation, Kazuhiro Hosono, Akihito Takeuchi, and Gen Tatara, J. Phys. Soc. Jpn. 79, 014708 (2010) .
【Contact】Dr. Hiori Kino(木野日織）
UV and visible photoactivity of titania:nature of reduced and doped TiO2 from first principle calculations
Prof. Gianfranco Pacchioni
【Date & Time】24 June 2010 (Thu) 16:15 - 17:00
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site / 並木地区MANA棟4Fセミナー室
【Speaker】Prof. Gianfranco Pacchioni
【Affiliation】Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca
【Title】UV and visible photoactivity of titania:nature of reduced and doped TiO2 from first principle calculations
【Abstract】
Titania is an essential component of new generation devices for photocatalysis and solar energy conversion. Its special behavior under illumination is at the basis of several practical applications like self-cleaning and self-sterilizing surfaces, superhydrophilicity, corrosion protection, etc. Most of these effects are observed under UV light and efforts are now oriented to the preparation of visible light photoactive titania. In this talk we will review the most recent advances in this field, and we will discuss in more detail the nature of doped TiO2 and of the interplay of intrinsic defects (like oxygen vacancies resulting in the formation of “Ti3+” ions) and states induced by transition and non-transition metal dopants like Cr, Sb, B, C, N, and F. The addition of heteroatoms, of crucial importance to improve the photactivity of the material, results in new states in the gap of titania and in paramagnetic centers. These centers may contribute to improve the photoactivity of the material under visible light but can also act as recombination centers for electrons and holes, thus resulting in a reduced activity. The description of these systems with advanced theoretical methods presents problems connected to the need to correctly reproduce the band gap of the material and the localized nature of the defects created by doping.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site / 並木地区MANA棟4Fセミナー室
【Speaker】Prof. Gianfranco Pacchioni
【Affiliation】Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca
【Title】UV and visible photoactivity of titania:nature of reduced and doped TiO2 from first principle calculations
【Abstract】
Titania is an essential component of new generation devices for photocatalysis and solar energy conversion. Its special behavior under illumination is at the basis of several practical applications like self-cleaning and self-sterilizing surfaces, superhydrophilicity, corrosion protection, etc. Most of these effects are observed under UV light and efforts are now oriented to the preparation of visible light photoactive titania. In this talk we will review the most recent advances in this field, and we will discuss in more detail the nature of doped TiO2 and of the interplay of intrinsic defects (like oxygen vacancies resulting in the formation of “Ti3+” ions) and states induced by transition and non-transition metal dopants like Cr, Sb, B, C, N, and F. The addition of heteroatoms, of crucial importance to improve the photactivity of the material, results in new states in the gap of titania and in paramagnetic centers. These centers may contribute to improve the photoactivity of the material under visible light but can also act as recombination centers for electrons and holes, thus resulting in a reduced activity. The description of these systems with advanced theoretical methods presents problems connected to the need to correctly reproduce the band gap of the material and the localized nature of the defects created by doping.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Roles of Mott physics in Semiconductor Impurity Bands and Copper-Oxide Superconductors
Prof. Hiroshi Kamimura (上村洸 教授)
【Date & Time】09 June 2010 (Wed) 3:30 pm - 5:00 pm
【Place】8F large seminar room, SENGEN site
【Speaker】Prof. Hiroshi Kamimura (上村洸 教授)
【Affiliation】Tokyo University of Science (東京理科大学)
【Title】Roles of Mott physics in Semiconductor Impurity Bands and Copper-Oxide Superconductors
【Abstract】
In this talk, I would like to propose that Mott physics due to electron-electron interactions plays a similar role in semiconductor impurity bands and copper oxide superconductors. In the impurity bands in doped semiconductors the interplay of disorder and electron-electron (e-e) interactions gives rise to the coexistence of spin-singlet and spin-triplet states in the strongly Anderson-localized regime just below the metal-insulator transition. As a result peculiar spin-dependent phenomena appear in various physical properties of doped semiconductors, such as specific heat, spin susceptibility, and magnetoresistance in the Anderson-localized regime.
In copper oxide (cuprate) superconductors, on the other hand, the interplay of Jahn-Teller Physics and Mott Physics plays important roles in giving rise to the coexistence of a metallic state and the local antiforromagnetic (AF) order. As a result the feature of Fermi surface in cuprates is the occurrences of Fermi-pockets constructed from the doped holes without the pseudogap hypothesis. In the second part of the present talk I will discuss why cuprates show Fermi pockets rather than a large Fermi surface with the pseudogap. This theoretical result will be compared with recent experimental results of angle-resolver photoemission spectroscopy (ARPES) in cuprates both below and above Tc.
【Contact】Dr. Takahisa Ohno(大野 隆央)
【Place】8F large seminar room, SENGEN site
【Speaker】Prof. Hiroshi Kamimura (上村洸 教授)
【Affiliation】Tokyo University of Science (東京理科大学)
【Title】Roles of Mott physics in Semiconductor Impurity Bands and Copper-Oxide Superconductors
【Abstract】
In this talk, I would like to propose that Mott physics due to electron-electron interactions plays a similar role in semiconductor impurity bands and copper oxide superconductors. In the impurity bands in doped semiconductors the interplay of disorder and electron-electron (e-e) interactions gives rise to the coexistence of spin-singlet and spin-triplet states in the strongly Anderson-localized regime just below the metal-insulator transition. As a result peculiar spin-dependent phenomena appear in various physical properties of doped semiconductors, such as specific heat, spin susceptibility, and magnetoresistance in the Anderson-localized regime.
In copper oxide (cuprate) superconductors, on the other hand, the interplay of Jahn-Teller Physics and Mott Physics plays important roles in giving rise to the coexistence of a metallic state and the local antiforromagnetic (AF) order. As a result the feature of Fermi surface in cuprates is the occurrences of Fermi-pockets constructed from the doped holes without the pseudogap hypothesis. In the second part of the present talk I will discuss why cuprates show Fermi pockets rather than a large Fermi surface with the pseudogap. This theoretical result will be compared with recent experimental results of angle-resolver photoemission spectroscopy (ARPES) in cuprates both below and above Tc.
【Contact】Dr. Takahisa Ohno(大野 隆央)
Modeling Ordered Phases using Compound Energy Formalism
Prof. Bo Sundman
【Date & Time】20 May 2010 (Thu), 13:30 - 15:00
【Place】8F large seminar room, Central Bldg., Sengen site
【Speaker】Professor Bo Sundman
【Affiliation】INSTN, CEA-Saclay, France
【Title】Modeling Ordered Phases using Compound Energy Formalism
【Abstract】
The thermodynamic modeling of chemical ordering in multicomponent alloys will be presented. First ordering in binary systems, like in FCC phases as in Al-Ni and Au-Cu and in BCC phases as in Al-Fe and Fe-Ti will be explained.
The modeling of ordering is very dependent on the use of first principle calculations to obtain enthalpies of formation for meta-stable ordered states. Then extrapolation of the ordering into ternary and higher order systems will be discussed. The approximation of the short range ordering contribution to the Gibbs energy in the Compound Energy Formalism will be explained. The modeling of ordered phases that never disorder, like s and m, will also be discussed.
References:
B Sundman, S G Fries and W A Oates, A Thermodynamic Assessment of the Au-Cu system, Calphad, 22 (1998) 335-354.
T Abe and B Sundman, A description of the effect of short range ordering in the compound energy formalism, Calphad 27 (2003) 403-408
N Dupin, S G Fries, J M Joubert, B Sundman, M H F Sluiter, Y Kawazoe and A Pasturel, Using first-principles results to calculate finite-temperature thermodynamic properties of the Nb-Ni m phase in the Bragg-Williams approximation, Phil Mag 86 (2006) 1631-1641
H.L. Lukas, S.G. Fries and B. Sundman, Computational Thermodynamics, Cambridge University Press, 2007
B Sundman, N Dupin, U Kattner, I Ohnuma and S G Fries, An assessment of the entire Al-Fe system with D03 ordering, Acta Materialia 57 (2009) 2896-2908.
【Contact】Dr. Taichi Abe(阿部太一)
【Place】8F large seminar room, Central Bldg., Sengen site
【Speaker】Professor Bo Sundman
【Affiliation】INSTN, CEA-Saclay, France
【Title】Modeling Ordered Phases using Compound Energy Formalism
【Abstract】
The thermodynamic modeling of chemical ordering in multicomponent alloys will be presented. First ordering in binary systems, like in FCC phases as in Al-Ni and Au-Cu and in BCC phases as in Al-Fe and Fe-Ti will be explained.
The modeling of ordering is very dependent on the use of first principle calculations to obtain enthalpies of formation for meta-stable ordered states. Then extrapolation of the ordering into ternary and higher order systems will be discussed. The approximation of the short range ordering contribution to the Gibbs energy in the Compound Energy Formalism will be explained. The modeling of ordered phases that never disorder, like s and m, will also be discussed.
References:
B Sundman, S G Fries and W A Oates, A Thermodynamic Assessment of the Au-Cu system, Calphad, 22 (1998) 335-354.
T Abe and B Sundman, A description of the effect of short range ordering in the compound energy formalism, Calphad 27 (2003) 403-408
N Dupin, S G Fries, J M Joubert, B Sundman, M H F Sluiter, Y Kawazoe and A Pasturel, Using first-principles results to calculate finite-temperature thermodynamic properties of the Nb-Ni m phase in the Bragg-Williams approximation, Phil Mag 86 (2006) 1631-1641
H.L. Lukas, S.G. Fries and B. Sundman, Computational Thermodynamics, Cambridge University Press, 2007
B Sundman, N Dupin, U Kattner, I Ohnuma and S G Fries, An assessment of the entire Al-Fe system with D03 ordering, Acta Materialia 57 (2009) 2896-2908.
【Contact】Dr. Taichi Abe(阿部太一)
First principles calculations of the σ and χ phases in Binary and Ternary Rhenium-based systems
Dr. Jean-Claude Crivello
【Date & Time】28 April 2010 (Wed), 13:30 - 15:00
【Place】6F small seminar room, Central Bldg., Sengen site
【Speaker】Dr. Jean-Claude Crivello
【Affiliation】CNRS – ICMPE – CMTR (Thiais, France)
【Title】First principles calculations of the σ and χ phases in Binary and Ternary Rhenium-based systems
【Abstract】
The topologically close packed phases appear in many important multi-components systems, like superalloys, in which refractory elements are added. The precipitation of these intermetallic compounds may cause problems due to their brittleness which affects the mechanical properties of the alloy, motivating the present study about their stability.
Systematic DFT calculations have been performed for the complete set of ordered configurations generated by distributing A or B elements in the σ and χ phases among the different sites for the four binary A–B systems, with A = {Nb, Ta, Mo, W} and B = Re. Moreover, the ternary -Cr-Mo-Re system has been investigated since the two binary Cr-Re and Mo-Re -phase are known for showing inverse Re sites preference: high coordination number (CN) sites in Cr-Re [1] and low CN in Mo-Re [2].
Total energies have been used in order to compute the atomic distribution at finite temperatures in the Bragg–Williams (BW) approximation. It is shown that the configurational entropy stabilizes the σ and χ phases in MoRe and WRe, while there are stable in NbRe and TaRe. Computed sites occupancies are in very good agreement with the experimental measurements. About the ternary Cr-Mo-Re -phase, this system presents a miscibility gap at low temperature and its Gibbs energy surface is convex above ~750K [3]. Re site preference is shown to change progressively in the ternary field when passing from Mo-Re to Cr-Re binary borders.
References
[1] M. Palumbo, T. Abe, C. Kocer, H. Murakami, H. Onodera, in preparation.
[2] J.-C. Crivello and J.-M. Joubert, J. Phys.: Condens. Matter 22 (2010) 035402.
[3] J.-C Crivello, M. Palumbo, T. Abe and J.-M. Joubert, in preparation.
【Contact】Dr. Taichi Abe(阿部太一)
【Place】6F small seminar room, Central Bldg., Sengen site
【Speaker】Dr. Jean-Claude Crivello
【Affiliation】CNRS – ICMPE – CMTR (Thiais, France)
【Title】First principles calculations of the σ and χ phases in Binary and Ternary Rhenium-based systems
【Abstract】
The topologically close packed phases appear in many important multi-components systems, like superalloys, in which refractory elements are added. The precipitation of these intermetallic compounds may cause problems due to their brittleness which affects the mechanical properties of the alloy, motivating the present study about their stability.
Systematic DFT calculations have been performed for the complete set of ordered configurations generated by distributing A or B elements in the σ and χ phases among the different sites for the four binary A–B systems, with A = {Nb, Ta, Mo, W} and B = Re. Moreover, the ternary -Cr-Mo-Re system has been investigated since the two binary Cr-Re and Mo-Re -phase are known for showing inverse Re sites preference: high coordination number (CN) sites in Cr-Re [1] and low CN in Mo-Re [2].
Total energies have been used in order to compute the atomic distribution at finite temperatures in the Bragg–Williams (BW) approximation. It is shown that the configurational entropy stabilizes the σ and χ phases in MoRe and WRe, while there are stable in NbRe and TaRe. Computed sites occupancies are in very good agreement with the experimental measurements. About the ternary Cr-Mo-Re -phase, this system presents a miscibility gap at low temperature and its Gibbs energy surface is convex above ~750K [3]. Re site preference is shown to change progressively in the ternary field when passing from Mo-Re to Cr-Re binary borders.
References
[1] M. Palumbo, T. Abe, C. Kocer, H. Murakami, H. Onodera, in preparation.
[2] J.-C. Crivello and J.-M. Joubert, J. Phys.: Condens. Matter 22 (2010) 035402.
[3] J.-C Crivello, M. Palumbo, T. Abe and J.-M. Joubert, in preparation.
【Contact】Dr. Taichi Abe(阿部太一)
Numerical simulations on effect of surface impedance in THz wave emission from intrinsic Josephson junctions
固有ジョセフソン接合のテラヘルツ波発振における表面インピーダンスの影響の数値シミュレーション
Dr. Yoshihiko Nonomura (野々村禎彦 博士)
【Date & Time】21 April 2010 (Wed) 3:30 pm - 5:00 pm
【Place】6F seminar room, SENGEN site
【Speaker】Dr. Yoshihiko Nonomura (野々村禎彦 博士)
【Affiliation】Particle Simulation and Thermodynamics Group, CMSC, NIMS (NIMS 計算科学センター 粒子・統計熱力学グループ)
【Title】Numerical simulations on effect of surface impedance in THz wave emission from intrinsic Josephson junctions
固有ジョセフソン接合のテラヘルツ波発振における表面インピーダンスの影響の数値シミュレーション
【Abstract】
Current-induced emission from intrinsic Josephson junctions such as mesa structure of BSCCO is one of promising candidates of continuous source of the electromagnetic waves with ~1 THz frequency. Recently such emission without external magnetic fields was observed, and theoretical models with the in-phase state or pi-phase-kink states were proposed. My numerical study revealed [1] that the in-phase state is stable only in a limited region f or rather small surface impedance Z<5, and that the pi-phase-kink states are stabilized for most parameter regions. I further studied emission in in-plane magnetic fields [2] and found that there exists a crossover for field profile of emission intensity for Z=50~60. For smaller Z the field profile has a nontrivial peak together with a dynamical phase transition between the pi-phase-kink and in-phase states, while for larger Z the field profile decreases monotonically. Such sharp dependence of the field profile of emission intensity on surface impedance may explain recent controversial experiments.
[1] Y. Nonomura, Phys. Rev. B 80, 140506(R) (2009).
[2] Y. Nonomura, arXiv:1003.4045.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】6F seminar room, SENGEN site
【Speaker】Dr. Yoshihiko Nonomura (野々村禎彦 博士)
【Affiliation】Particle Simulation and Thermodynamics Group, CMSC, NIMS (NIMS 計算科学センター 粒子・統計熱力学グループ)
【Title】Numerical simulations on effect of surface impedance in THz wave emission from intrinsic Josephson junctions
固有ジョセフソン接合のテラヘルツ波発振における表面インピーダンスの影響の数値シミュレーション
【Abstract】
Current-induced emission from intrinsic Josephson junctions such as mesa structure of BSCCO is one of promising candidates of continuous source of the electromagnetic waves with ~1 THz frequency. Recently such emission without external magnetic fields was observed, and theoretical models with the in-phase state or pi-phase-kink states were proposed. My numerical study revealed [1] that the in-phase state is stable only in a limited region f or rather small surface impedance Z<5, and that the pi-phase-kink states are stabilized for most parameter regions. I further studied emission in in-plane magnetic fields [2] and found that there exists a crossover for field profile of emission intensity for Z=50~60. For smaller Z the field profile has a nontrivial peak together with a dynamical phase transition between the pi-phase-kink and in-phase states, while for larger Z the field profile decreases monotonically. Such sharp dependence of the field profile of emission intensity on surface impedance may explain recent controversial experiments.
[1] Y. Nonomura, Phys. Rev. B 80, 140506(R) (2009).
[2] Y. Nonomura, arXiv:1003.4045.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Density functional based global geometry optimization and their application to clusters with cage-like structure
Prof. Stefan Goedecker
【Date & Time】9 April 2010 (Fri) 15:30 - 16:15
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site / 並木地区MANA棟4Fセミナー室
【Speaker】Prof. Stefan Goedecker
【Affiliation】University of Basel, Switzerland
【Title】Density functional based global geometry optimization and their application to clusters with cage-like structure
【Abstract】
Global geometry optimization allows to find the global minimum of the potential energy surface of condensed matter systems. The ground state structure of molecules, nano-systems and crystalline materials can thus be predicted. I will first introduce the two essential methodological ingredients of our global geometry optimization, namely the minima hopping algorithm and the BigDFT density functional (DFT) program which uses wavelets as basis functions.
I will next show that global optimization on the DFT potential energy landscape is easier than on the potential energy landscape of more approximate schemes such as force fields.
Finally I will show structures that were obtained by global optimization for charged clusters, endohedral metal doped silicon clusters, boron fullerenes and model crystalline structures.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site / 並木地区MANA棟4Fセミナー室
【Speaker】Prof. Stefan Goedecker
【Affiliation】University of Basel, Switzerland
【Title】Density functional based global geometry optimization and their application to clusters with cage-like structure
【Abstract】
Global geometry optimization allows to find the global minimum of the potential energy surface of condensed matter systems. The ground state structure of molecules, nano-systems and crystalline materials can thus be predicted. I will first introduce the two essential methodological ingredients of our global geometry optimization, namely the minima hopping algorithm and the BigDFT density functional (DFT) program which uses wavelets as basis functions.
I will next show that global optimization on the DFT potential energy landscape is easier than on the potential energy landscape of more approximate schemes such as force fields.
Finally I will show structures that were obtained by global optimization for charged clusters, endohedral metal doped silicon clusters, boron fullerenes and model crystalline structures.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Supersolid phase of three-dimensional spin and lattice-boson models /
3次元磁性体および格子上のボソンモデルの超固体状態
Dr. Hiroaki Ueda (植田浩明博士)
【Date & Time】8 April 2010 (Thu), 15:00 pm -
【Place】8F seminar room, Central Bldg., Sengen site
【Speaker】Dr. Hiroaki Ueda (植田浩明博士)
【Affiliation】Yukawa Institute for Theoretical Physics, Kyoto University (京都大学基礎物理学研究所)
【Title】Supersolid phase of three-dimensional spin and lattice-boson models /
3次元磁性体および格子上のボソンモデルの超固体状態
【Abstract】
We investigate the stability of solid and supersolid (SS) phases of three-dimensional spin and hardcore-boson models on a body-centered cubic lattice. This lattice boson model was applied to a study of the low-temperature physics in 4He, and Liu and Fisher concluded the SS phase for 4He within the mean-field approximation. To see quantum effects on the stability of the SS phase, we reconsider this model from the viewpoint of Bose-Einstein condensation of vacancies (interstitials) in the solid. We find that quantum fluctuations can be strong enough to destabilize not only the solid phase but also the SS phase for a parameter set believed to be appropriate to 4He.
【Contact】Dr. Hiroyuki Yamase(山瀬博之)
【Place】8F seminar room, Central Bldg., Sengen site
【Speaker】Dr. Hiroaki Ueda (植田浩明博士)
【Affiliation】Yukawa Institute for Theoretical Physics, Kyoto University (京都大学基礎物理学研究所)
【Title】Supersolid phase of three-dimensional spin and lattice-boson models /
3次元磁性体および格子上のボソンモデルの超固体状態
【Abstract】
We investigate the stability of solid and supersolid (SS) phases of three-dimensional spin and hardcore-boson models on a body-centered cubic lattice. This lattice boson model was applied to a study of the low-temperature physics in 4He, and Liu and Fisher concluded the SS phase for 4He within the mean-field approximation. To see quantum effects on the stability of the SS phase, we reconsider this model from the viewpoint of Bose-Einstein condensation of vacancies (interstitials) in the solid. We find that quantum fluctuations can be strong enough to destabilize not only the solid phase but also the SS phase for a parameter set believed to be appropriate to 4He.
【Contact】Dr. Hiroyuki Yamase(山瀬博之)
Transport, heat, and anharmonic interactions
Prof. Nicola Marzari
【Date & Time】11 March 2010 (Thu) 15:45 - 16:30
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site / 並木地区MANA棟4Fセミナー室
【Speaker】Prof. Nicola Marzari
【Affiliation】Director of Materials Modeling Laboratory, Department of Materials, University of Oxford
【Title】Transport, heat, and anharmonic interactions
【Abstract】
Vibrational excitations in solids are key to understanding electronic and thermal transport in bulk or nanostructured materials, and are probed directly by Raman, infrared, and neutron scattering. They can also be calculated directly from first-principles by applying perturbation theory to the electronic ground state; density-functional perturbation theory (DFPT) provides results of great accuracy for a very broad class of materials. We use DFPT to calculate phonon spectra and electron-phonon and phonon-phonon interactions, and to characterize the structure and the electronic and thermal transport of complex materials and nanostructures, where low-dimensionality can impose thermalization bottlenecks that are key hurdles to overcome in the current miniaturization trend. Examples will cover 1) the thermomechanical properties of bulk and low-dimensionality materials 2) finite-temperature Raman characterization of free-standing and strained graphene; 3) breakdown of ballistic transport in carbon nanotube interconnects; and 4) thermal conductivity in Si-Ge alloys and superlattices.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site / 並木地区MANA棟4Fセミナー室
【Speaker】Prof. Nicola Marzari
【Affiliation】Director of Materials Modeling Laboratory, Department of Materials, University of Oxford
【Title】Transport, heat, and anharmonic interactions
【Abstract】
Vibrational excitations in solids are key to understanding electronic and thermal transport in bulk or nanostructured materials, and are probed directly by Raman, infrared, and neutron scattering. They can also be calculated directly from first-principles by applying perturbation theory to the electronic ground state; density-functional perturbation theory (DFPT) provides results of great accuracy for a very broad class of materials. We use DFPT to calculate phonon spectra and electron-phonon and phonon-phonon interactions, and to characterize the structure and the electronic and thermal transport of complex materials and nanostructures, where low-dimensionality can impose thermalization bottlenecks that are key hurdles to overcome in the current miniaturization trend. Examples will cover 1) the thermomechanical properties of bulk and low-dimensionality materials 2) finite-temperature Raman characterization of free-standing and strained graphene; 3) breakdown of ballistic transport in carbon nanotube interconnects; and 4) thermal conductivity in Si-Ge alloys and superlattices.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Hydrogen production by a bio-inspired model catalyst/electrode system
Prof. Annabella Selloni
【Date & Time】11 March 2010 (Thu) 15:00 - 15:45
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site / 並木地区MANA棟4Fセミナー室
【Speaker】Prof. Annabella Selloni
【Affiliation】Department of Chemistry, Princeton University
【Title】Hydrogen production by a bio-inspired model catalyst/electrode system
【Abstract】
We present First-Principles Molecular-Dynamics (FPMD) simulations of H2 production by the [FeFe]H cluster of the active site of the di-iron hydrogenases supported on a FeS2(100) surface in acidified water. The study is carried out in steps of increasing complexity, starting from the bare catalyst, first in vacuo and next in water, and then considering the catalyst coupled to the electrode surface, again first in vacuo and then in aqueous solution. Important findings are that a modified isomer of the [FeFe]H cluster can form a stable link to the surface, and there is a low-activation-energy pathway for hydrogen production from acidified water by the functionalized pyrite surface. This work is done in collaboration with Dr. Federico Zipoli, Prof. Morrel H. Cohen, and Prof. Roberto Car.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site / 並木地区MANA棟4Fセミナー室
【Speaker】Prof. Annabella Selloni
【Affiliation】Department of Chemistry, Princeton University
【Title】Hydrogen production by a bio-inspired model catalyst/electrode system
【Abstract】
We present First-Principles Molecular-Dynamics (FPMD) simulations of H2 production by the [FeFe]H cluster of the active site of the di-iron hydrogenases supported on a FeS2(100) surface in acidified water. The study is carried out in steps of increasing complexity, starting from the bare catalyst, first in vacuo and next in water, and then considering the catalyst coupled to the electrode surface, again first in vacuo and then in aqueous solution. Important findings are that a modified isomer of the [FeFe]H cluster can form a stable link to the surface, and there is a low-activation-energy pathway for hydrogen production from acidified water by the functionalized pyrite surface. This work is done in collaboration with Dr. Federico Zipoli, Prof. Morrel H. Cohen, and Prof. Roberto Car.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
The editing mechanism of aminoacyl-tRNA synthetases operates by a hybrid ribozyme/protein catalyst
Dr. Yohsuke Hagiwara(萩原陽介氏)
【Date & Time】3 March 2010 (Wed), 13:30 am - 14:30 am
【Place】6F seminar room, Central Bldg., Sengen site
【Speaker】Dr. Yohsuke Hagiwara(萩原陽介氏)
【Affiliation】Tsukuba Univ. (筑波大学数理物質科学研究科物理学専攻)
【Title】The editing mechanism of aminoacyl-tRNA synthetases operates by a hybrid ribozyme/protein catalyst
【Abstract】
Aminoacyl-tRNA synthetases (aaRSs) are critical for the translational process, catalyzing the attachment of specific amino acids to their cognate tRNAs. To ensure formation of the correct aminoacyl-tRNA, and thereby enhance the reliability of translation, several aaRSs have an editing capability that hinders formation of mis-aminoacylated tRNAs. We investigated theoretically the mechanism of the editing reaction for a class I enzyme, leucyl-tRNA synthetase (LeuRS), complexed with a mis-aminoacylated tRNALeu, employing ab initio hybrid quantum mechanical/molecular mechanical (QM/MM) potentials with all-electron density functional theory for the part of the QM calculations, in conjunction with molecular dynamics simulations. It is shown that the water molecule that acts as the nucleophile in the editing reaction is activated by a 3'-hydroxyl group at the 3'-end of tRNALeu, and that the O2' atom of the leaving group of the substrate is capped by one of the water’s hydrogen atoms. Thus, it is shown that editing is a self-cleavage reaction of the tRNA and so it is the tRNA, and not the protein, that drives the reaction. The protein does, however, have an important stabilizing effect on some high-energy intermediates along the reaction path, which is more efficient than the ribozyme would be alone. This indicates that editing is achieved by a novel “hybrid ribozyme/protein catalyst”. Analysis of existing experimental data and additional modeling shows that this ribozymal mechanism appears to be widespread, occurring in the ribosome as well as in other aaRSs. It also suggests transitional forms that could have played an important role in the RNA world hypothesis for the origin of life.
Reference: J. Am.Chem. Soc., DOI: 10.1021/ja9095208.
【Contact】Dr. Hiori Kino(木野日織）
【Place】6F seminar room, Central Bldg., Sengen site
【Speaker】Dr. Yohsuke Hagiwara(萩原陽介氏)
【Affiliation】Tsukuba Univ. (筑波大学数理物質科学研究科物理学専攻)
【Title】The editing mechanism of aminoacyl-tRNA synthetases operates by a hybrid ribozyme/protein catalyst
【Abstract】
Aminoacyl-tRNA synthetases (aaRSs) are critical for the translational process, catalyzing the attachment of specific amino acids to their cognate tRNAs. To ensure formation of the correct aminoacyl-tRNA, and thereby enhance the reliability of translation, several aaRSs have an editing capability that hinders formation of mis-aminoacylated tRNAs. We investigated theoretically the mechanism of the editing reaction for a class I enzyme, leucyl-tRNA synthetase (LeuRS), complexed with a mis-aminoacylated tRNALeu, employing ab initio hybrid quantum mechanical/molecular mechanical (QM/MM) potentials with all-electron density functional theory for the part of the QM calculations, in conjunction with molecular dynamics simulations. It is shown that the water molecule that acts as the nucleophile in the editing reaction is activated by a 3'-hydroxyl group at the 3'-end of tRNALeu, and that the O2' atom of the leaving group of the substrate is capped by one of the water’s hydrogen atoms. Thus, it is shown that editing is a self-cleavage reaction of the tRNA and so it is the tRNA, and not the protein, that drives the reaction. The protein does, however, have an important stabilizing effect on some high-energy intermediates along the reaction path, which is more efficient than the ribozyme would be alone. This indicates that editing is achieved by a novel “hybrid ribozyme/protein catalyst”. Analysis of existing experimental data and additional modeling shows that this ribozymal mechanism appears to be widespread, occurring in the ribosome as well as in other aaRSs. It also suggests transitional forms that could have played an important role in the RNA world hypothesis for the origin of life.
Reference: J. Am.Chem. Soc., DOI: 10.1021/ja9095208.
【Contact】Dr. Hiori Kino(木野日織）
Computer Simulation in the Physical & Life Sciences : From Chemistry to Materials & the Nano-Bio-Med Frontier
Prof. Michael L. Klein, FRS
【Date & Time】21 January 2010 (Thu) 16:00 - 17:00
【Place】8F large seminar room (８階中セミナー室), SENGEN site
【Speaker】Prof. Michael L. Klein, FRS
【Affiliation】Director of the Institute of Computational Molecular Science in the College of Science & Technology, Temple University
【Title】Computer Simulation in the Physical & Life Sciences : From Chemistry to Materials & the Nano-Bio-Med Frontier
【Abstract】
The past decade has seen enormous progress in the broad application of computation to topical problems in science and engineering. By selected examples I will illustrate the current status of the field that employs computer simulation methodologies based on the principles of statistical mechanics to problems at the interface between materials science and chemical biology. The prospects for future applications in the biomedical arena will also be touched on, albeit briefly.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】8F large seminar room (８階中セミナー室), SENGEN site
【Speaker】Prof. Michael L. Klein, FRS
【Affiliation】Director of the Institute of Computational Molecular Science in the College of Science & Technology, Temple University
【Title】Computer Simulation in the Physical & Life Sciences : From Chemistry to Materials & the Nano-Bio-Med Frontier
【Abstract】
The past decade has seen enormous progress in the broad application of computation to topical problems in science and engineering. By selected examples I will illustrate the current status of the field that employs computer simulation methodologies based on the principles of statistical mechanics to problems at the interface between materials science and chemical biology. The prospects for future applications in the biomedical arena will also be touched on, albeit briefly.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)