CMS seminar2010
GPU Utilization Method and GPU Acceleration of Diffusion Monte Carlo Method
Mr. Teppei Ono
【Date & Time】30 November 2010 (Tue), 16:00 -- 17:00
【Place】4F seminar room (#431-2), MANA Bldg., Namiki site
【Speaker】Mr. Teppei Ono
【Affiliation】SQUARE ENIX CO., LTD.
【Title】GPU Utilization Method and GPU Acceleration of Diffu
【Abstract】
In recent years, graphics processor units (GPU) have achieved remarkable performance improvements, and it has become important to utilize them as new computing resources in the field of computational science. The problem of calculation accuracy, which had been a problem, was solved by the appearance of GPUs capable of double-precision computations, and its utilization in the field of electronic state calculation became realistic. It is fully expected that numerical calculation using some kind of accelerator will become the mainstream in the future. We need to understand the characteristics of each architecture and choose the appropriate use. In this lecture, the procedures, parallelization means, and optimization methods for using GPUs for scientific calculations are explained, and an example of the diffusion Monte Carlo method using GPUs is introduced as an example of using GPUs for first-principles calculations. We also propose an example of a flexible source code description method with a view to supporting new architectures in the future.
【Contact】Dr. Yoshitaka Tateyama
【Place】4F seminar room (#431-2), MANA Bldg., Namiki site
【Speaker】Mr. Teppei Ono
【Affiliation】SQUARE ENIX CO., LTD.
【Title】GPU Utilization Method and GPU Acceleration of Diffu
【Abstract】
In recent years, graphics processor units (GPU) have achieved remarkable performance improvements, and it has become important to utilize them as new computing resources in the field of computational science. The problem of calculation accuracy, which had been a problem, was solved by the appearance of GPUs capable of double-precision computations, and its utilization in the field of electronic state calculation became realistic. It is fully expected that numerical calculation using some kind of accelerator will become the mainstream in the future. We need to understand the characteristics of each architecture and choose the appropriate use. In this lecture, the procedures, parallelization means, and optimization methods for using GPUs for scientific calculations are explained, and an example of the diffusion Monte Carlo method using GPUs is introduced as an example of using GPUs for first-principles calculations. We also propose an example of a flexible source code description method with a view to supporting new architectures in the future.
【Contact】Dr. Yoshitaka Tateyama
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
【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
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
【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
【Place】4F seminar room (#409-10), Collaborative Research Bldg., Namiki site
【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
Recent developments in theory of superfluidity
Prof. Yusuke Kato
【Date & Time】06 July 2010 (Tue), 15:30 -
【Place】8F large seminar room, Sengen site
【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
【Place】8F large seminar room, Sengen site
【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
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
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
【Place】8F large seminar room, Sengen site
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
Microscopic Theory of Generation and Detection of Spin Current
Prof. Gen Tatara
【Date & Time】28 June 2010 (Mon), 14:00 - 15:30
【Place】8F large seminar room, Sengen site
【Speaker】Prof. Gen Tatara
【Affiliation】Department of Physics, Tokyo Metropolitan Univ.
【Title】Microscopic Theory of Generation and Detection of Spin Current
【Abstract】
In recent years, the physics of spin flow (spin flow) has attracted much attention from the viewpoint of device application (spintronics), and has been extensively studied. Spin flow applications require the creation and transport of spin flows and the establishment of current-spin flow transformations that are essential for contacts with existing electronics. At present, many interesting proposals have already been made for all of them, and spin flow control has been established experimentally. For example, in a ferromagnetic metal, the current necessarily accompanies the spin flow, and in a nonmagnetic material, the spin flow can be generated by using the spin Hall effect using the electric field and the spin orbit interaction. In addition, it is known that the motion of magnetization is also accompanied by the generation of spin flow, and when this is used, it is possible to inject spin flow into a nonmagnetic body by a junction of a ferromagnetic body and a nonmagnetic body (spin pumping). Recently, spin flow generation (spin Seebeck effect) using light of circular deflection and temperature gradient is also realized. It has also been confirmed that the spin flow-current transformation is possible by using the spin-orbit interaction, and this inverse spin Hall effect is frequently used for the detection of spin flows.
In the lecture, the progress of theoretical understanding of these phenomena will be introduced and issues in spin flow control will be discussed.
Reference
[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
【Place】8F large seminar room, Sengen site
【Speaker】Prof. Gen Tatara
【Affiliation】Department of Physics, Tokyo Metropolitan Univ.
【Title】Microscopic Theory of Generation and Detection of Spin Current
【Abstract】
In recent years, the physics of spin flow (spin flow) has attracted much attention from the viewpoint of device application (spintronics), and has been extensively studied. Spin flow applications require the creation and transport of spin flows and the establishment of current-spin flow transformations that are essential for contacts with existing electronics. At present, many interesting proposals have already been made for all of them, and spin flow control has been established experimentally. For example, in a ferromagnetic metal, the current necessarily accompanies the spin flow, and in a nonmagnetic material, the spin flow can be generated by using the spin Hall effect using the electric field and the spin orbit interaction. In addition, it is known that the motion of magnetization is also accompanied by the generation of spin flow, and when this is used, it is possible to inject spin flow into a nonmagnetic body by a junction of a ferromagnetic body and a nonmagnetic body (spin pumping). Recently, spin flow generation (spin Seebeck effect) using light of circular deflection and temperature gradient is also realized. It has also been confirmed that the spin flow-current transformation is possible by using the spin-orbit interaction, and this inverse spin Hall effect is frequently used for the detection of spin flows.
In the lecture, the progress of theoretical understanding of these phenomena will be introduced and issues in spin flow control will be discussed.
Reference
[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
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
【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
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site
【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
Roles of Mott physics in Semiconductor Impurity Bands and Copper-Oxide Superconductors
Prof. Hiroshi Kamimura
【Date & Time】09 June 2010 (Wed) 3:30 pm - 5:00 pm
【Place】8F large seminar room, SENGEN site
【Speaker】Prof. Hiroshi Kamimura
【Affiliation】Tokyo University of Science
【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
【Place】8F large seminar room, SENGEN site
【Speaker】Prof. Hiroshi Kamimura
【Affiliation】Tokyo University of Science
【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
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
【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
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
【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
Numerical simulations on effect of surface impedance in THz wave emission from intrinsic Josephson junctions
Dr. Yoshihiko Nonomura
【Date & Time】21 April 2010 (Wed) 3:30 pm - 5:00 pm
【Place】6F seminar room, SENGEN site
【Speaker】Dr. Yoshihiko Nonomura
【Affiliation】Particle Simulation and Thermodynamics Group, CMSC, NIMS
【Title】Numerical simulations on effect of surface impedance in THz wave emission from intrinsic Josephson junctions
【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
【Place】6F seminar room, SENGEN site
【Speaker】Dr. Yoshihiko Nonomura
【Affiliation】Particle Simulation and Thermodynamics Group, CMSC, NIMS
【Title】Numerical simulations on effect of surface impedance in THz wave emission from intrinsic Josephson junctions
【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
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
【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
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site
【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
Supersolid phase of three-dimensional spin and lattice-boson models /
Dr. Hiroaki Ueda
【Date & Time】8 April 2010 (Thu), 15:00 pm -
【Place】8F seminar room, Central Bldg., Sengen site
【Speaker】Dr. Hiroaki Ueda
【Affiliation】Yukawa Institute for Theoretical Physics, Kyoto University
【Title】Supersolid phase of three-dimensional spin and lattice-boson models /
【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
【Place】8F seminar room, Central Bldg., Sengen site
【Speaker】Dr. Hiroaki Ueda
【Affiliation】Yukawa Institute for Theoretical Physics, Kyoto University
【Title】Supersolid phase of three-dimensional spin and lattice-boson models /
【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
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
【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
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site
【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
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
【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
【Place】4F seminar room (#431-2), MANA Bldg. Namiki site
【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
The editing mechanism of aminoacyl-tRNA synthetases operates by a hybrid ribozyme/protein catalyst
Dr. Yohsuke Hagiwara
【Date & Time】3 March 2010 (Wed), 13:30 am - 14:30 am
【Place】6F seminar room, Central Bldg., Sengen site
【Speaker】Dr. Yohsuke Hagiwara
【Affiliation】Tsukuba Univ.
【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
【Place】6F seminar room, Central Bldg., Sengen site
【Speaker】Dr. Yohsuke Hagiwara
【Affiliation】Tsukuba Univ.
【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
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, 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
【Place】8F large seminar room, 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