CMSセミナー2008
Electronic Structure of New Iron Arsenide Superconductors
Dr. Zlata Pchelkina
【Date & Time】18 December 2008 (Thur), 3:30 pm - 5:00 pm
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Zlata Pchelkina
【Affiliation】Institute for Metal Physics, Ural Division, Russian Academy of Sciences
【Title】Electronic Structure of New Iron Arsenide Superconductors
【Abstract】
In the beginning of 2008 the iron oxypnictides, a new family of superconductors, have been discovered starting with the famous work of H. Hosono group [1]. At present the several classes of these compounds are known: Re111 (Re=La,Ce,Pr,Nd,Sm) with parent compound LaO1-xFxFeAs and Tc about 40-55K; A122 (A=Ba,Sr) with parent system Ba1-xKxFe2As2 and Tc about 38K; Li1-xFeAs system with Tc=18K and Sr1-xLaxFFeAs compound with Tc=36K. It was also found that FeSe undergoes superconducting transition at temperature Tc=8K which can be increased to Tc=27K by applying high pressure.
In this talk an overview of different classes of FeAs based superconductors will be given, the basic physical properties and phase diagrams will be described. The results of electronic structure calculations for the parent compounds Re111 [2], Ba(Sr)122 [3], LiFeAs [4] and Ca(Sr)111 [5] will be presented.
[1] Y. Kamihara et al., J. Am. Chem. Soc. 130, 3296 (2008).
[2] I. A. Nekrasov, Z. V. Pchelkina, M. V. Sadovskii,Pis'ma Zh. Eksp. Teor. Fiz. 87, 647 (2008).
[3] I. A. Nekrasov, Z. V. Pchelkina, M. V. Sadovskii,Pis'ma Zh. Eksp. Teor. Fiz. 88, 155 (2008).
[4] I. A. Nekrasov, Z. V. Pchelkina, M. V. Sadovskii,Pis'ma Zh. Eksp. Teor. Fiz. 88, 621 (2008).
[5] I. A. Nekrasov, Z. V. Pchelkina, M. V. Sadovskii,Pis'ma Zh. Eksp. Teor. Fiz. 88, 777 (2008).
【Contact】Dr. Igor Solovyev
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Zlata Pchelkina
【Affiliation】Institute for Metal Physics, Ural Division, Russian Academy of Sciences
【Title】Electronic Structure of New Iron Arsenide Superconductors
【Abstract】
In the beginning of 2008 the iron oxypnictides, a new family of superconductors, have been discovered starting with the famous work of H. Hosono group [1]. At present the several classes of these compounds are known: Re111 (Re=La,Ce,Pr,Nd,Sm) with parent compound LaO1-xFxFeAs and Tc about 40-55K; A122 (A=Ba,Sr) with parent system Ba1-xKxFe2As2 and Tc about 38K; Li1-xFeAs system with Tc=18K and Sr1-xLaxFFeAs compound with Tc=36K. It was also found that FeSe undergoes superconducting transition at temperature Tc=8K which can be increased to Tc=27K by applying high pressure.
In this talk an overview of different classes of FeAs based superconductors will be given, the basic physical properties and phase diagrams will be described. The results of electronic structure calculations for the parent compounds Re111 [2], Ba(Sr)122 [3], LiFeAs [4] and Ca(Sr)111 [5] will be presented.
[1] Y. Kamihara et al., J. Am. Chem. Soc. 130, 3296 (2008).
[2] I. A. Nekrasov, Z. V. Pchelkina, M. V. Sadovskii,Pis'ma Zh. Eksp. Teor. Fiz. 87, 647 (2008).
[3] I. A. Nekrasov, Z. V. Pchelkina, M. V. Sadovskii,Pis'ma Zh. Eksp. Teor. Fiz. 88, 155 (2008).
[4] I. A. Nekrasov, Z. V. Pchelkina, M. V. Sadovskii,Pis'ma Zh. Eksp. Teor. Fiz. 88, 621 (2008).
[5] I. A. Nekrasov, Z. V. Pchelkina, M. V. Sadovskii,Pis'ma Zh. Eksp. Teor. Fiz. 88, 777 (2008).
【Contact】Dr. Igor Solovyev
Strongly correlated electrons in heterostructures:transport, magnetism, and superconductivity
Dr. Satoshi Okamoto
【Date & Time】8 December 2008 (Mon), 3:30 pm - 5:00 pm
【Place】4F seminar room, Collaborative Res. Bldg., Namiki site
【Speaker】Dr. Satoshi Okamoto
【Affiliation】Materials Science and Technology Division, Oak Ridge National Lab., USA
【Title】Strongly correlated electrons in heterostructures:transport, magnetism, and superconductivity
【Abstract】
Study of artificial heterostructures involving transition-metal oxides is one of the main topics of current materials science [1]. Among various oxides, of particular interest are correlated-electron systems which exhibit a variety of phenomena such as high-Tc superconductivity in cuprates. Correlated heterostructures are expected to become fundamental building blocks of future oxide electronics utilizing the novel properties of the oxides. Thus, understanding of the correlated electron behaviors at surfaces and interfaces is of crucial importance. In this talk, I will present the recent theoretical development in this field, including the following three topics.
1. Mott-insulator/metal interface [2,3]. It is shown that the spectral function in the interacting region is modified by the coupling with the metallic region, resulting in rather non-linear transport behavior.
2. Surface magnetic behavior of double-exchange ferromagnet for manganites [4]. The magnetic moment in abut-three-unit-cell-wide surface layers is found to decrease rapidly with increasing temperature. Possible improvement of the tunneling magnetoresistance effect is expected by supressing this behavior.
3. Superlattices of high-Tc cuprates [5]. We examine the possibility of enhanced superconductivity in heterostructures involving both the underdoped cuprates and overdoped cuprates by applying the cluster dynamical-mean-field methods.
Work in ORNL is supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy.
[1] For example, A. Ohtomo et al., Nature (London) 419, 378 (2002).
[2] S. Okamoto (unpublished).
[3] S. Okamoto, Phys. Rev. Lett. 101, 116807 (2008).
[4] S. Okamoto (unpublished).
[5] S. Okamoto and T. A. Maier, Phys. Rev. Lett. 101, 156401 (2008).
【Contact】Dr. Masao Arai(新井正男)
【Place】4F seminar room, Collaborative Res. Bldg., Namiki site
【Speaker】Dr. Satoshi Okamoto
【Affiliation】Materials Science and Technology Division, Oak Ridge National Lab., USA
【Title】Strongly correlated electrons in heterostructures:transport, magnetism, and superconductivity
【Abstract】
Study of artificial heterostructures involving transition-metal oxides is one of the main topics of current materials science [1]. Among various oxides, of particular interest are correlated-electron systems which exhibit a variety of phenomena such as high-Tc superconductivity in cuprates. Correlated heterostructures are expected to become fundamental building blocks of future oxide electronics utilizing the novel properties of the oxides. Thus, understanding of the correlated electron behaviors at surfaces and interfaces is of crucial importance. In this talk, I will present the recent theoretical development in this field, including the following three topics.
1. Mott-insulator/metal interface [2,3]. It is shown that the spectral function in the interacting region is modified by the coupling with the metallic region, resulting in rather non-linear transport behavior.
2. Surface magnetic behavior of double-exchange ferromagnet for manganites [4]. The magnetic moment in abut-three-unit-cell-wide surface layers is found to decrease rapidly with increasing temperature. Possible improvement of the tunneling magnetoresistance effect is expected by supressing this behavior.
3. Superlattices of high-Tc cuprates [5]. We examine the possibility of enhanced superconductivity in heterostructures involving both the underdoped cuprates and overdoped cuprates by applying the cluster dynamical-mean-field methods.
Work in ORNL is supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy.
[1] For example, A. Ohtomo et al., Nature (London) 419, 378 (2002).
[2] S. Okamoto (unpublished).
[3] S. Okamoto, Phys. Rev. Lett. 101, 116807 (2008).
[4] S. Okamoto (unpublished).
[5] S. Okamoto and T. A. Maier, Phys. Rev. Lett. 101, 156401 (2008).
【Contact】Dr. Masao Arai(新井正男)
Algorithms and applications of QM/MM hybrid simulations for elucidation of functional mechanisms and structural-based rational design of biological molecules
Prof. Martin J. Field
【Date & Time】18 November 2008 (Tue), 1:30 pm - 3:00 pm
【Place】4F seminar room, MANA Bldg., Namiki Site
【Speaker】Prof. Martin J. Field
【Affiliation】Laboratoire de Dynamique Moleculaire, Institut de Biologie Structurale, France
【Title】Algorithms and applications of QM/MM hybrid simulations for elucidation of functional mechanisms and structural-based rational design of biological molecules
【Abstract】
Interactions of biological macromolecules such as proteins, nucleic acids are the source of biological functions. However, it is difficult to perform theoretical investigations of such interactions based on their electronic structures, because of huge number of atoms and thermal fluctuations. To investigate these systems, quantum mechanics/molecular mechanics (QM/MM) calculations are utilized, in which the system is divided into QM and MM atoms. Here, QM regions correspond to active sites to be investigated, and are described on the basis of the quantum mechanics theory. MM regions correspond to the remainder of the system, and are described at the molecular mechanics level.
In this seminar, recent progresses in QM/MM hybrid calculations, in particular, of biological macromolecules, are presented, including pharmaceutical issues. Our original calculation methods and their applications into proteins and structure-based rational drug design of therapeutic regents on the basis of our original algorithms and systems for QM/MM hybrid simulations are also discussed.
【Contact】Dr. Hiori Kino(木野日織）
【Place】4F seminar room, MANA Bldg., Namiki Site
【Speaker】Prof. Martin J. Field
【Affiliation】Laboratoire de Dynamique Moleculaire, Institut de Biologie Structurale, France
【Title】Algorithms and applications of QM/MM hybrid simulations for elucidation of functional mechanisms and structural-based rational design of biological molecules
【Abstract】
Interactions of biological macromolecules such as proteins, nucleic acids are the source of biological functions. However, it is difficult to perform theoretical investigations of such interactions based on their electronic structures, because of huge number of atoms and thermal fluctuations. To investigate these systems, quantum mechanics/molecular mechanics (QM/MM) calculations are utilized, in which the system is divided into QM and MM atoms. Here, QM regions correspond to active sites to be investigated, and are described on the basis of the quantum mechanics theory. MM regions correspond to the remainder of the system, and are described at the molecular mechanics level.
In this seminar, recent progresses in QM/MM hybrid calculations, in particular, of biological macromolecules, are presented, including pharmaceutical issues. Our original calculation methods and their applications into proteins and structure-based rational drug design of therapeutic regents on the basis of our original algorithms and systems for QM/MM hybrid simulations are also discussed.
【Contact】Dr. Hiori Kino(木野日織）
GWA method with LSDA+U (U+ GWA) and applications to transition metal oxides
Prof. Takeo Fujiwara(藤原毅夫教授)
【Date & Time】10 November 2008 (Mon), 3:30 pm - 5:00 pm
【Place】4F seminar room, Collaborative Res. Bldg., Namiki site
【Speaker】Prof. Takeo Fujiwara(藤原毅夫教授)
【Affiliation】University of Tokyo, JST-CREST(東京大学大学総合教育研究センター, JST-CREST)
【Title】GWA method with LSDA+U (U+ GWA) and applications to transition metal oxides
【Abstract】
We propose a novel GW approximation (GWA) method named U+ GWA, where we start GWA with more localized wave-functions obtained by LSDA+U method. Then U+ GWAtogether with GWA are applied to several transitionmetal oxides, MnO,NiO, V2O3 and LaMO3 (M = Ti ∼ Cu) with eigenvalue-only self-consistency. The band gaps, magnetic moments and energy spectra in these materials show an excellent agreement with the experimentally observed results. The method of the unique choice of U values will be discussed in details. The criterion whether we should adopt GWA or U+ GWA will be discussed and assessed with the help of the off-diagonal elements of the self-energy.
【Contact】Dr. Masao Arai(新井正男)
【Place】4F seminar room, Collaborative Res. Bldg., Namiki site
【Speaker】Prof. Takeo Fujiwara(藤原毅夫教授)
【Affiliation】University of Tokyo, JST-CREST(東京大学大学総合教育研究センター, JST-CREST)
【Title】GWA method with LSDA+U (U+ GWA) and applications to transition metal oxides
【Abstract】
We propose a novel GW approximation (GWA) method named U+ GWA, where we start GWA with more localized wave-functions obtained by LSDA+U method. Then U+ GWAtogether with GWA are applied to several transitionmetal oxides, MnO,NiO, V2O3 and LaMO3 (M = Ti ∼ Cu) with eigenvalue-only self-consistency. The band gaps, magnetic moments and energy spectra in these materials show an excellent agreement with the experimentally observed results. The method of the unique choice of U values will be discussed in details. The criterion whether we should adopt GWA or U+ GWA will be discussed and assessed with the help of the off-diagonal elements of the self-energy.
【Contact】Dr. Masao Arai(新井正男)
Topological insulators and surface states / トポロジカルな絶縁体と表面状態
Prof. Shuichi Murakami(村上修一准教授)
【Date & Time】6 November 2008 (Thur), 3:00 pm - 4:30 pm
【Place】4F seminar room, Collaborative Res. Bldg., Namiki site
【Speaker】Prof. Shuichi Murakami(村上修一准教授)
【Affiliation】Department of Physics, Tokyo Institute of Technology(東京工業大学大学院理工学研究科物性物理学専攻)
【Title】Topological insulators and surface states / トポロジカルな絶縁体と表面状態
【Abstract】
The quantum spin Hall (QSH) system has been intensively studied in recent years, as a topic related with the spin Hall effect. While it is a spin analogue of the quantum Hall system, it occurs under zero magnetic field, and the spin-orbit coupling in the system plays the role of spin-dependent "magnetic field". This system is insulating in the bulk, whereas the edge states (in 2D) or the surface states (in 3D) are gapless, carrying spin currents. These edge or surface states remain gapless, being topologically protected against nonmagnetic impurities and surface roughness. In my talk we present our recent research results together with related theories and experiments.
スピンホール効果の研究から発展して最近、量子スピンホール系の物理が理論・実験両面から注目されている。これは量子ホール系のスピン版とみなせるが磁場は必要とせず、物質に内在するスピン軌道相互作用がスピンに依存した有効磁場の役目を果たす。この系はバルクでは絶縁体であるが、エッジ状態（２次元系）や表面状態（３次元系）がギャップレスでスピン流を運ぶ。このエッジ状態・表面状態はトポロジカルに保護されており、非磁性不純物や表面のラフネス等があってもギャップレスのままである。本講演ではこの効果に関する理論・実験を、最近の我々の研究結果を交えて解説する。
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】4F seminar room, Collaborative Res. Bldg., Namiki site
【Speaker】Prof. Shuichi Murakami(村上修一准教授)
【Affiliation】Department of Physics, Tokyo Institute of Technology(東京工業大学大学院理工学研究科物性物理学専攻)
【Title】Topological insulators and surface states / トポロジカルな絶縁体と表面状態
【Abstract】
The quantum spin Hall (QSH) system has been intensively studied in recent years, as a topic related with the spin Hall effect. While it is a spin analogue of the quantum Hall system, it occurs under zero magnetic field, and the spin-orbit coupling in the system plays the role of spin-dependent "magnetic field". This system is insulating in the bulk, whereas the edge states (in 2D) or the surface states (in 3D) are gapless, carrying spin currents. These edge or surface states remain gapless, being topologically protected against nonmagnetic impurities and surface roughness. In my talk we present our recent research results together with related theories and experiments.
スピンホール効果の研究から発展して最近、量子スピンホール系の物理が理論・実験両面から注目されている。これは量子ホール系のスピン版とみなせるが磁場は必要とせず、物質に内在するスピン軌道相互作用がスピンに依存した有効磁場の役目を果たす。この系はバルクでは絶縁体であるが、エッジ状態（２次元系）や表面状態（３次元系）がギャップレスでスピン流を運ぶ。このエッジ状態・表面状態はトポロジカルに保護されており、非磁性不純物や表面のラフネス等があってもギャップレスのままである。本講演ではこの効果に関する理論・実験を、最近の我々の研究結果を交えて解説する。
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Pomeranchuk instability in correlated electron systems
Dr. Hiroyuki Yamase(山瀬博之博士)
【Date & Time】30 October 2008 (Thur), 3:00 pm - 4:30 pm
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Hiroyuki Yamase(山瀬博之博士)
【Affiliation】Materials Interdisciplinary G, Innovative Materials Engineering Lab., NIMS(NIMS材料ラボ 融合領域研究G)
【Title】Pomeranchuk instability in correlated electron systems
【Abstract】
The spontaneous Fermi surface symmetry breaking, the so-called Pomeranchuk instability, is a fundamentally new concept in the physics of correlated electron systems [1,2]. This instability breaks the point-group symmetry of the underlying lattice structure.
In this talk, I discuss the most fundamental aspect of Pomeranchuk instability by performing the exact analysis of a pure forward scattering model. Current understanding of Pomeranchuk instability for high-temperature cuprate superconductors and strontium ruthenates is also reviewed.
[1] H. Yamase and H. Kohno, JPSJ 69, 332 (2000); 69, 2151 (2000).
[2] C. J. Halboth and W. Metzner, PRL 85, 5162 (2000).
【Contact】Dr. Akihiro Tanaka(田中秋広）
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Hiroyuki Yamase(山瀬博之博士)
【Affiliation】Materials Interdisciplinary G, Innovative Materials Engineering Lab., NIMS(NIMS材料ラボ 融合領域研究G)
【Title】Pomeranchuk instability in correlated electron systems
【Abstract】
The spontaneous Fermi surface symmetry breaking, the so-called Pomeranchuk instability, is a fundamentally new concept in the physics of correlated electron systems [1,2]. This instability breaks the point-group symmetry of the underlying lattice structure.
In this talk, I discuss the most fundamental aspect of Pomeranchuk instability by performing the exact analysis of a pure forward scattering model. Current understanding of Pomeranchuk instability for high-temperature cuprate superconductors and strontium ruthenates is also reviewed.
[1] H. Yamase and H. Kohno, JPSJ 69, 332 (2000); 69, 2151 (2000).
[2] C. J. Halboth and W. Metzner, PRL 85, 5162 (2000).
【Contact】Dr. Akihiro Tanaka(田中秋広）
Novel effects in spin-dependent transport
Prof. Renat Sabirianov
【Date & Time】31 July 2008 (Thur), 10:30 am - 12:00 am
【Place】6F seminar room, Sengen site
【Speaker】Prof. Renat Sabirianov
【Affiliation】Dept. of Physics, Univ. of Nebraska / ISSP, Univ. of Tokyo
【Title】Novel effects in spin-dependent transport
【Abstract】
Spin dependent transport in a synergistic combination with novel nanoscale magnetic and ferroelectric structures can be used to manipulate spin-dependent currents yielding new paradigms for device operation. I will discuss recent advances in spintronics concentrating on the discovery of new magnetoresistive phenomena: (1) ballistic anisotropic magnetoresistance (BAMR), a quantized change in the ballistic conductance of the nanowires and nanocontact with magnetization direction, (2) tunneling anisotropic magnetoresistance (TAMR) in magnetic break junctions, and (3) voltage induced magnetoresistance (MR) sign reversal. Transition metal oxides exhibit large changes in conductivity when an appropriate bias is applied, which make them promising for memory devices. The change in the MR associated with this transition has not been, however, explored, but may uncover fascinating physics. We have recently observed a MR sign reversal associated with the bias dependent on/off state in a Ni/NiO/CoNi/NiO/Co magnetic tunnel junction (MTJ) in nanowire geometry at T=1.5K. This behavior may be explained by a metal-insulator transition driven by a charge accumulation controlled by applied bias voltage.
【Contact】Dr. Igor Solovyev
【Place】6F seminar room, Sengen site
【Speaker】Prof. Renat Sabirianov
【Affiliation】Dept. of Physics, Univ. of Nebraska / ISSP, Univ. of Tokyo
【Title】Novel effects in spin-dependent transport
【Abstract】
Spin dependent transport in a synergistic combination with novel nanoscale magnetic and ferroelectric structures can be used to manipulate spin-dependent currents yielding new paradigms for device operation. I will discuss recent advances in spintronics concentrating on the discovery of new magnetoresistive phenomena: (1) ballistic anisotropic magnetoresistance (BAMR), a quantized change in the ballistic conductance of the nanowires and nanocontact with magnetization direction, (2) tunneling anisotropic magnetoresistance (TAMR) in magnetic break junctions, and (3) voltage induced magnetoresistance (MR) sign reversal. Transition metal oxides exhibit large changes in conductivity when an appropriate bias is applied, which make them promising for memory devices. The change in the MR associated with this transition has not been, however, explored, but may uncover fascinating physics. We have recently observed a MR sign reversal associated with the bias dependent on/off state in a Ni/NiO/CoNi/NiO/Co magnetic tunnel junction (MTJ) in nanowire geometry at T=1.5K. This behavior may be explained by a metal-insulator transition driven by a charge accumulation controlled by applied bias voltage.
【Contact】Dr. Igor Solovyev
Quantum simulations by ab initio path integral molecular dynamics
第一原理経路積分分子動力学法による量子シミュレーション
Dr. Motoyuki Shiga(志賀基之博士)
【Date & Time】14 July 2008 (Mon), 3:30 pm - 5:00 pm
【Place】8F larger seminar room, Sengen site
【Speaker】Dr. Motoyuki Shiga(志賀基之博士)
【Affiliation】Japan Atomic Energy Agency (JAEA)(日本原子力研究開発機構)
【Title】Quantum simulations by ab initio path integral molecular dynamics
第一原理経路積分分子動力学法による量子シミュレーション
【Abstract】
Nuclear quantum effect such as zero point vibration or tunneling is important in molecular systems containing light atoms like hydrogen, and it is considered to have influence on the chemical and physical properties. In this presentation, I would like to introduce the methodology of ab initio calculations including nuclear quantum effect by path integral molecular dynamics, and report some application studies on the isotope effect of hydrogen bonds.
水素など軽い元素をもつ分子系には零点振動やトンネル効果といった原子核の量子性が大切であり、分子の化学的・物理的特性に影響を与えていると考えられている。本講演では、経路積分分子動力学法により原子核の量子ゆらぎを含めた第一原理計算の方法論を紹介し、水素結合の同位体効果を中心とした応用研究について発表したい。
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】8F larger seminar room, Sengen site
【Speaker】Dr. Motoyuki Shiga(志賀基之博士)
【Affiliation】Japan Atomic Energy Agency (JAEA)(日本原子力研究開発機構)
【Title】Quantum simulations by ab initio path integral molecular dynamics
第一原理経路積分分子動力学法による量子シミュレーション
【Abstract】
Nuclear quantum effect such as zero point vibration or tunneling is important in molecular systems containing light atoms like hydrogen, and it is considered to have influence on the chemical and physical properties. In this presentation, I would like to introduce the methodology of ab initio calculations including nuclear quantum effect by path integral molecular dynamics, and report some application studies on the isotope effect of hydrogen bonds.
水素など軽い元素をもつ分子系には零点振動やトンネル効果といった原子核の量子性が大切であり、分子の化学的・物理的特性に影響を与えていると考えられている。本講演では、経路積分分子動力学法により原子核の量子ゆらぎを含めた第一原理計算の方法論を紹介し、水素結合の同位体効果を中心とした応用研究について発表したい。
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Photo-induced Tomonaga-Luttinger-like liquid in a one-dimensional Mott insulator
Dr. Takashi Oka(岡隆史博士)
【Date & Time】2 July 2008 (Wed), 3:30 pm - 5:00 pm
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Takashi Oka(岡隆史博士)
【Affiliation】Department of Physics, University of Tokyo(東京大学大学院理学系研究科物理学専攻)
【Title】Photo-induced Tomonaga-Luttinger-like liquid in a one-dimensional Mott insulator
【Abstract】
We theoretically study the non-equilibrium quantum phase transition in strongly correlated electron systemswhen strong AC electric fields are applied tothe Mott insulator.
The time-dependent density matrix renormalization group method is used to calculate the nonlinear optical conductivity for the half-filled one-dimensional Hubbard model, where we have found an emergence ofmetallic states that have a linear dispersion within the energy gap. This indicates that the photo-doped carriers behave collectively as in the Tomonaga-Luttinger liquid. A non-equilibrium phase diagram for the photo-induced insulator-to-metal transition is then proposed.
We further show that the numerical result is similar to an analytic result for an effective Dirac model, where the Floquet method is employed to incorporate the effect of strong electric fields.
【Contact】Dr. Akihiro Tanaka(田中秋広）
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Takashi Oka(岡隆史博士)
【Affiliation】Department of Physics, University of Tokyo(東京大学大学院理学系研究科物理学専攻)
【Title】Photo-induced Tomonaga-Luttinger-like liquid in a one-dimensional Mott insulator
【Abstract】
We theoretically study the non-equilibrium quantum phase transition in strongly correlated electron systemswhen strong AC electric fields are applied tothe Mott insulator.
The time-dependent density matrix renormalization group method is used to calculate the nonlinear optical conductivity for the half-filled one-dimensional Hubbard model, where we have found an emergence ofmetallic states that have a linear dispersion within the energy gap. This indicates that the photo-doped carriers behave collectively as in the Tomonaga-Luttinger liquid. A non-equilibrium phase diagram for the photo-induced insulator-to-metal transition is then proposed.
We further show that the numerical result is similar to an analytic result for an effective Dirac model, where the Floquet method is employed to incorporate the effect of strong electric fields.
【Contact】Dr. Akihiro Tanaka(田中秋広）
A first-principles molecular dynamics program PHASE - program structure and parallelization methods -
第一原理分子動力学法プログラムPHASEの構造と並列化方法
Dr. Takahiro Yamasaki(山崎隆浩博士)
【Date & Time】1 July 2008 (Tue), 1:30 pm - 3:00 pm
【Place】5F seminar room, Sengen site
【Speaker】Dr. Takahiro Yamasaki(山崎隆浩博士)
【Affiliation】FUJITSU Laboratories Ltd.(富士通研究所)
【Title】A first-principles molecular dynamics program PHASE - program structure and parallelization methods -
第一原理分子動力学法プログラムPHASEの構造と並列化方法
【Abstract】
PHASE is a first-principles molecular dynamics program that optimizes geometories and calculates electronic structures of materials using pseudopotentials and plane wave basis based on the density functional theory. It has had been developed in a MITI project, then successivey in a MEXT project. It has calculational functions of XPS, positoron life time evaluation, STM images, lattice vibrations, and reaction path searchings. PHASE runs on personal computers, cluster workstations, and large scale computers like the Earth Simulator. It is effectively parallelized in a MPI-SMP hybrid way, and can run very large scale calculations of 10,000 atom order on the Earth Simulator. It is tuned not only for vector processors but also for scalar ones. The program is consist of almost fifty hierarchical modules. In this seminar, we would explain roles of the principal modules and the methodology of parallelization. Parallelization problems for peta-scale computers would also be discussed.
第一原理分子動力学法プログラムPHASEは密度汎関数法に基づき擬ポテンシャルと平面波を使って固体の構造および電子状態を求めるプログラムであり、1993年から通産省のプロジェクトで、その後引き続き文部科学省のプロジェクトで開発されてきた。PHASEは、XPS、陽電子寿命、STM像、振動解析、反応経路探索などの計算機能も持つ。PHASEはPCから、クラスター計算機、地球シミュレータなどの大規模計算機に対応している。地球シミュレータでは、プログラムはMPIとSMPで二重に効率的に並列化されており、10,000原子程度の大規模計算が可能である。ベクトル計算機だけでなく、スカラー計算機用にも最適化されている。プログラムは階層化された50個程度のモジュールから構成されている。当日は、主要なモジュールプログラムの役割と、並列化手法について説明する。またペタスケール計算機に向けた最適化の課題についても述べる。
【Contact】Dr. Hiori Kino(木野日織）
【Place】5F seminar room, Sengen site
【Speaker】Dr. Takahiro Yamasaki(山崎隆浩博士)
【Affiliation】FUJITSU Laboratories Ltd.(富士通研究所)
【Title】A first-principles molecular dynamics program PHASE - program structure and parallelization methods -
第一原理分子動力学法プログラムPHASEの構造と並列化方法
【Abstract】
PHASE is a first-principles molecular dynamics program that optimizes geometories and calculates electronic structures of materials using pseudopotentials and plane wave basis based on the density functional theory. It has had been developed in a MITI project, then successivey in a MEXT project. It has calculational functions of XPS, positoron life time evaluation, STM images, lattice vibrations, and reaction path searchings. PHASE runs on personal computers, cluster workstations, and large scale computers like the Earth Simulator. It is effectively parallelized in a MPI-SMP hybrid way, and can run very large scale calculations of 10,000 atom order on the Earth Simulator. It is tuned not only for vector processors but also for scalar ones. The program is consist of almost fifty hierarchical modules. In this seminar, we would explain roles of the principal modules and the methodology of parallelization. Parallelization problems for peta-scale computers would also be discussed.
第一原理分子動力学法プログラムPHASEは密度汎関数法に基づき擬ポテンシャルと平面波を使って固体の構造および電子状態を求めるプログラムであり、1993年から通産省のプロジェクトで、その後引き続き文部科学省のプロジェクトで開発されてきた。PHASEは、XPS、陽電子寿命、STM像、振動解析、反応経路探索などの計算機能も持つ。PHASEはPCから、クラスター計算機、地球シミュレータなどの大規模計算機に対応している。地球シミュレータでは、プログラムはMPIとSMPで二重に効率的に並列化されており、10,000原子程度の大規模計算が可能である。ベクトル計算機だけでなく、スカラー計算機用にも最適化されている。プログラムは階層化された50個程度のモジュールから構成されている。当日は、主要なモジュールプログラムの役割と、並列化手法について説明する。またペタスケール計算機に向けた最適化の課題についても述べる。
【Contact】Dr. Hiori Kino(木野日織）
Low-energy models for Molecular Solids: θ- and κ-(BEDT-TTF)2X
Dr. Kazuma Nakamura(中村和磨博士)
【Date & Time】26 June 2008 (Thur), 1:00 pm - 2:30 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Kazuma Nakamura(中村和磨博士)
【Affiliation】Department of Applied Physics, University of Tokyo(東京大学大学院工学系研究科物理工学専攻)
【Title】Low-energy models for Molecular Solids: θ- and κ-(BEDT-TTF)2X
【Abstract】
Aiming at a deeper understanding of physics and chemistry of organic molecular solids, we perform first-principles analyses for two different types of (BEDT-TTF)2X; θ- and κ-type compounds. These compounds have strong two-dimensional anisotropy and the conducting layer relevant to the low-energy physics near the Fermi energy consists of aligned BEDT-TTF molecules. In spite of the structural similarity, the physics of the θ and κ compounds is completely different; in the θ type, puzzling coexistence of two different charge-ordering fluctuations in metallic phase is observed near charge-ordered and spin-Peierls phases. On the other hand, the κ compound shows typical Mott physics exhibiting a phase diagram involving antiferromagnetic Mott insulator, genuine Mott insulator with spin liquid nature, paramagnetic metal, and superconductor phases. The origin of such a diversity and mechanisms of stabilizing each phase themselves are intriguing questions to be answered.
I will present ab initio downfolded low-energy effective models of the θ and κ compounds. By the downfolding procedure, we derive model parameters such as transfer integrals and interaction terms, with the help of the maximally-localized-Wannier-function technique and the constrained random-phase-approximation methodology. Novel expressions for entire three-dimensional data of the screened Coulomb and exchange interactions are first derived. The difference between the resulting models for the θ and κ compounds is discussed with particular focus on a substantial difference in the range of the screened Coulomb interaction, together with their comparisons with the screened interactions of several types of transition metal oxides.
【Contact】Dr. Hiori Kino(木野日織）
【Place】6F seminar room, Sengen site
【Speaker】Dr. Kazuma Nakamura(中村和磨博士)
【Affiliation】Department of Applied Physics, University of Tokyo(東京大学大学院工学系研究科物理工学専攻)
【Title】Low-energy models for Molecular Solids: θ- and κ-(BEDT-TTF)2X
【Abstract】
Aiming at a deeper understanding of physics and chemistry of organic molecular solids, we perform first-principles analyses for two different types of (BEDT-TTF)2X; θ- and κ-type compounds. These compounds have strong two-dimensional anisotropy and the conducting layer relevant to the low-energy physics near the Fermi energy consists of aligned BEDT-TTF molecules. In spite of the structural similarity, the physics of the θ and κ compounds is completely different; in the θ type, puzzling coexistence of two different charge-ordering fluctuations in metallic phase is observed near charge-ordered and spin-Peierls phases. On the other hand, the κ compound shows typical Mott physics exhibiting a phase diagram involving antiferromagnetic Mott insulator, genuine Mott insulator with spin liquid nature, paramagnetic metal, and superconductor phases. The origin of such a diversity and mechanisms of stabilizing each phase themselves are intriguing questions to be answered.
I will present ab initio downfolded low-energy effective models of the θ and κ compounds. By the downfolding procedure, we derive model parameters such as transfer integrals and interaction terms, with the help of the maximally-localized-Wannier-function technique and the constrained random-phase-approximation methodology. Novel expressions for entire three-dimensional data of the screened Coulomb and exchange interactions are first derived. The difference between the resulting models for the θ and κ compounds is discussed with particular focus on a substantial difference in the range of the screened Coulomb interaction, together with their comparisons with the screened interactions of several types of transition metal oxides.
【Contact】Dr. Hiori Kino(木野日織）
Pudding-mold type band as the origin of large thermopower in transition metal oxides
Prof. Ryotaro Arita(有田亮太郎准教授)
【Date & Time】9 May 2008 (Fri), 10:30 am - 12:00 am
【Place】8F large seminar room, Sengen site
【Speaker】Prof. Ryotaro Arita(有田亮太郎准教授)
【Affiliation】Department of Applied Physics, University of Tokyo(東京大学大学院工学系研究科物理工学専攻)
【Title】Pudding-mold type band as the origin of large thermopower in transition metal oxides
【Abstract】
Conversion of temperature differences directly into electricity is one of the most fascinating phenomena in condensed matter physics. Designing and searching for good thermoelectric materials indeed have a long history of extensive studies due to the scientific interest and potential technological importance.
Hitherto, it has been believed that the coexistence of low resistivity and large thermopower is difficult to realize, so that the main target thermoelectric materials have been various insulators or semiconductors. More recently, the focus of interest shifted however to thermoelectrical metals, where one is searching for exceptionally large power factors. NaxCoO2 and LiRh2O4 are in fact good examples of such interesting thermoelectric metals.
Here we propose that a peculiar shape of conduction bands plays an important role to realize the coexistence of large conductivity and thermopower.
We first examine this idea for NaxCoO2 and LiRh2O4 by the Boltzmann equation approach based on the local density approximation (LDA). We then step forward to the combination of LDA and the dynamical mean field theory (LDA+DMFT) for LiRh2O4, a 3D frustrated paramagnetic metal for which DMFT is expected to be a good approximation. We find that the experimental values of the large thermopower are successfully reproduced. We also simulate how the power factor can be much further enhanced through doping.
【Contact】Dr. Igor Solovyev
【Place】8F large seminar room, Sengen site
【Speaker】Prof. Ryotaro Arita(有田亮太郎准教授)
【Affiliation】Department of Applied Physics, University of Tokyo(東京大学大学院工学系研究科物理工学専攻)
【Title】Pudding-mold type band as the origin of large thermopower in transition metal oxides
【Abstract】
Conversion of temperature differences directly into electricity is one of the most fascinating phenomena in condensed matter physics. Designing and searching for good thermoelectric materials indeed have a long history of extensive studies due to the scientific interest and potential technological importance.
Hitherto, it has been believed that the coexistence of low resistivity and large thermopower is difficult to realize, so that the main target thermoelectric materials have been various insulators or semiconductors. More recently, the focus of interest shifted however to thermoelectrical metals, where one is searching for exceptionally large power factors. NaxCoO2 and LiRh2O4 are in fact good examples of such interesting thermoelectric metals.
Here we propose that a peculiar shape of conduction bands plays an important role to realize the coexistence of large conductivity and thermopower.
We first examine this idea for NaxCoO2 and LiRh2O4 by the Boltzmann equation approach based on the local density approximation (LDA). We then step forward to the combination of LDA and the dynamical mean field theory (LDA+DMFT) for LiRh2O4, a 3D frustrated paramagnetic metal for which DMFT is expected to be a good approximation. We find that the experimental values of the large thermopower are successfully reproduced. We also simulate how the power factor can be much further enhanced through doping.
【Contact】Dr. Igor Solovyev
Quantum Monte Carlo Simulation of VBS States
2次元VBS状態のモンテカルロシミュレーション
Prof. Naoki Kawashima(川島直輝准教授)
【Date & Time】24 April 2008 (Thur), 3:30 pm - 5:00 pm
【Place】8F larger seminar room, Sengen site
【Speaker】Prof. Naoki Kawashima(川島直輝准教授)
【Affiliation】Institute for Solid State Physics (ISSP), University of Tokyo(東京大学物性研究所)
【Title】Quantum Monte Carlo Simulation of VBS States
2次元VBS状態のモンテカルロシミュレーション
【Abstract】
We consider SU(N) generalization of the standard Heisenberg model. In other words, we regard operators S in the ordinary SU(2) Heisenberg Hamiltonian as the generators of SU(N) rotation rather than SU(2). We define the model on a bipartite lattice and use different representation for two sublattices: some representation for the sublattice A and its conjugate for the sublattice B. There is an interesting conjecture [1] for this very simple model, i.e., there is a transition from the Neel state to the VBS state as N is increased, and the nature of the VBS state changes periodically depending on the rank of the representation (=n). A similar conjecture for the one dimensional case is wellknown as Haldane's conjecture and has been confirmed by numerical calculations and other techniques. For the fundamental representation (n=1), we confirmed that there is a transition to the VBS state. [2]
Our recent calculations [3] further revealed that (1) in the fundamental representation, the plaquette type VBS pattern is as likely as the columnar VBS pattern, and U(1)-like behavior is observed, and that (2) the VBS pattern n=2 or above is vanishing or very small. The U(1)-like behavior is later observed in other models. [4,5] A related calculation on the quasi-one-dimensional biquadratic Heisenberg model [6] will also be discussed.
[1] N. Read and S. Sachdev, Nucl. Phys. B316, 609 (1989).
[2] K. Harada, N. Kawashima, and M. Troyer, Phys. Rev. Lett. 90, 117203 (2003).
[3] N. Kawashima and Y. Tanabe, Phys. Rev. Lett. 98, 057202 (2007).
[4] K. S. Beach and A. W. Sandvik, Phys. Rev. Lett. 99, 047202 (2007).
[5] M. Tsukamoto, K. Harada, and N. Kawashima, unpublished.
[6] K. Harada, N. Kawashima, and M. Troyer, J. Phys. Soc. Jpn. 76, 013703 (2007).
ハイゼンベルクモデルはよく研究されたモデルであるが，このモデルの対称性である SU(2) 対称性を SU(N) 対称性に拡張したモデルを考える．つまり，ハミルトニアンの表式はそのままにしておいて，その中にでてくる通常は SU(2) 回転の生成子であるスピン演算子をSU(N) 回転の生成子とみなすのである．ただし，格子は2次元 bipartite 格子とし，B格子上のスピン変数はA格子上のスピン変数が属する既約表現とは共役な既約表現に属するとする．このシンプルなモデルについて非常に面白い予想がある．[1] すなわち，N を増やしていくとネール状態からVBS状態への転移があり，更にVBS状態のパターンが表現によって周期的に変化する，というものである．同様の予言は，1次元 SU(2) モデルの場合にはハルデーン予想としておなじみのものであり，その正しいことも数値計算そのほかによって確かめられている．2次元 SU(N) モデルの場合にスピンの大きさに対応するのは，既約表現をヤング図であらわしたときの列の数 n である．実際に n=1 の場合にはこの予想が正しいことが量子モンテカルロ法による計算で確かめられている．[2]
我々が更に計算を行った結果，新たにふたつのことが分かった．[3]（1）n=1 のVBS基底状態が必ずしもコラムナーVBSだけでなく，プラケットVBS状態も同様に確からしく，実際にはこれらがほぼ縮退しており，少なくとも近似的には U(1) 的な対称性がみられること，（2）n=2 以上のVBS状態が観測されないこと，である．また，（1）はその後 SU(N) モデルだけでなく，量子ダイマーモデルに近い4体相互作用のある S=1/2 ハイゼンベルクモデルなどでも観察されている．[4,5] これと関連して，最近我々が行った準1次元 S=1 biquadratic 系に関する計算結果 [6] も紹介したい．
【Contact】Dr. Yoshihiko Nonomura (野々村禎彦)
【Place】8F larger seminar room, Sengen site
【Speaker】Prof. Naoki Kawashima(川島直輝准教授)
【Affiliation】Institute for Solid State Physics (ISSP), University of Tokyo(東京大学物性研究所)
【Title】Quantum Monte Carlo Simulation of VBS States
2次元VBS状態のモンテカルロシミュレーション
【Abstract】
We consider SU(N) generalization of the standard Heisenberg model. In other words, we regard operators S in the ordinary SU(2) Heisenberg Hamiltonian as the generators of SU(N) rotation rather than SU(2). We define the model on a bipartite lattice and use different representation for two sublattices: some representation for the sublattice A and its conjugate for the sublattice B. There is an interesting conjecture [1] for this very simple model, i.e., there is a transition from the Neel state to the VBS state as N is increased, and the nature of the VBS state changes periodically depending on the rank of the representation (=n). A similar conjecture for the one dimensional case is wellknown as Haldane's conjecture and has been confirmed by numerical calculations and other techniques. For the fundamental representation (n=1), we confirmed that there is a transition to the VBS state. [2]
Our recent calculations [3] further revealed that (1) in the fundamental representation, the plaquette type VBS pattern is as likely as the columnar VBS pattern, and U(1)-like behavior is observed, and that (2) the VBS pattern n=2 or above is vanishing or very small. The U(1)-like behavior is later observed in other models. [4,5] A related calculation on the quasi-one-dimensional biquadratic Heisenberg model [6] will also be discussed.
[1] N. Read and S. Sachdev, Nucl. Phys. B316, 609 (1989).
[2] K. Harada, N. Kawashima, and M. Troyer, Phys. Rev. Lett. 90, 117203 (2003).
[3] N. Kawashima and Y. Tanabe, Phys. Rev. Lett. 98, 057202 (2007).
[4] K. S. Beach and A. W. Sandvik, Phys. Rev. Lett. 99, 047202 (2007).
[5] M. Tsukamoto, K. Harada, and N. Kawashima, unpublished.
[6] K. Harada, N. Kawashima, and M. Troyer, J. Phys. Soc. Jpn. 76, 013703 (2007).
ハイゼンベルクモデルはよく研究されたモデルであるが，このモデルの対称性である SU(2) 対称性を SU(N) 対称性に拡張したモデルを考える．つまり，ハミルトニアンの表式はそのままにしておいて，その中にでてくる通常は SU(2) 回転の生成子であるスピン演算子をSU(N) 回転の生成子とみなすのである．ただし，格子は2次元 bipartite 格子とし，B格子上のスピン変数はA格子上のスピン変数が属する既約表現とは共役な既約表現に属するとする．このシンプルなモデルについて非常に面白い予想がある．[1] すなわち，N を増やしていくとネール状態からVBS状態への転移があり，更にVBS状態のパターンが表現によって周期的に変化する，というものである．同様の予言は，1次元 SU(2) モデルの場合にはハルデーン予想としておなじみのものであり，その正しいことも数値計算そのほかによって確かめられている．2次元 SU(N) モデルの場合にスピンの大きさに対応するのは，既約表現をヤング図であらわしたときの列の数 n である．実際に n=1 の場合にはこの予想が正しいことが量子モンテカルロ法による計算で確かめられている．[2]
我々が更に計算を行った結果，新たにふたつのことが分かった．[3]（1）n=1 のVBS基底状態が必ずしもコラムナーVBSだけでなく，プラケットVBS状態も同様に確からしく，実際にはこれらがほぼ縮退しており，少なくとも近似的には U(1) 的な対称性がみられること，（2）n=2 以上のVBS状態が観測されないこと，である．また，（1）はその後 SU(N) モデルだけでなく，量子ダイマーモデルに近い4体相互作用のある S=1/2 ハイゼンベルクモデルなどでも観察されている．[4,5] これと関連して，最近我々が行った準1次元 S=1 biquadratic 系に関する計算結果 [6] も紹介したい．
【Contact】Dr. Yoshihiko Nonomura (野々村禎彦)
Effect of defects on the structure, electronic structure, and dielectric properties of HfO2
Dr. Eric J. Cockayne
【Date & Time】16 April 2008 (Wed), 3:30 pm - 5:00 pm
【Place】8F larger seminar room, Sengen site
【Speaker】Dr. Eric J. Cockayne
【Affiliation】Ceramics Division, National Institute of Standards and Technology (NIST), USA
【Title】Effect of defects on the structure, electronic structure, and dielectric properties of HfO2
【Abstract】
This talk details the results of first-principles density functional theory studies of the effect of various defects on the structure, electronic structure, and dielectric properties of HfO2. The defects studied include oxygen vacancies, ionic substitutions, interstitials, and combinations of defects. Most defects cause a larger permittivity due to a variety of factors; the most significant enhancement occurs if the tetragonal or cubic phase of HfO2 is stabilized with respect to the monoclinic phase. The effect of Al substitution on Si-SiO2-HfO2 gate stacks is also investigated, and discussed in terms of a dipole model.
【Contact】Dr. Naoto Umezawa (梅澤直人)
【Place】8F larger seminar room, Sengen site
【Speaker】Dr. Eric J. Cockayne
【Affiliation】Ceramics Division, National Institute of Standards and Technology (NIST), USA
【Title】Effect of defects on the structure, electronic structure, and dielectric properties of HfO2
【Abstract】
This talk details the results of first-principles density functional theory studies of the effect of various defects on the structure, electronic structure, and dielectric properties of HfO2. The defects studied include oxygen vacancies, ionic substitutions, interstitials, and combinations of defects. Most defects cause a larger permittivity due to a variety of factors; the most significant enhancement occurs if the tetragonal or cubic phase of HfO2 is stabilized with respect to the monoclinic phase. The effect of Al substitution on Si-SiO2-HfO2 gate stacks is also investigated, and discussed in terms of a dipole model.
【Contact】Dr. Naoto Umezawa (梅澤直人)
Wavelets as basis functions for electronic structure calculations and their implementation in the ABINIT code
Prof. Stefan Goedecker
【Date & Time】17 March 2008 (Mon), 10:30 am - 12:00 am
【Place】8F larger seminar room, Sengen site
【Speaker】Prof. Stefan Goedecker
【Affiliation】Department of Physics and Astronomy, University of Basel
【Title】Wavelets as basis functions for electronic structure calculations and their implementation in the ABINIT code
【Abstract】
Wavelets are a relatively new class of mathematical functions and I will describe how they can be used as a basis set in density functional electronic structure calculations. Wavelets offer many advantages since they are adaptive, orthogonal and localized both in real and Fourier space. I will present performance comparisons with plane wave codes and some applications.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】8F larger seminar room, Sengen site
【Speaker】Prof. Stefan Goedecker
【Affiliation】Department of Physics and Astronomy, University of Basel
【Title】Wavelets as basis functions for electronic structure calculations and their implementation in the ABINIT code
【Abstract】
Wavelets are a relatively new class of mathematical functions and I will describe how they can be used as a basis set in density functional electronic structure calculations. Wavelets offer many advantages since they are adaptive, orthogonal and localized both in real and Fourier space. I will present performance comparisons with plane wave codes and some applications.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Role of randomness in martensitic transformation
乱雑性のマルテンサイト変態における役割
Dr. Tetsuro Suzuki(鈴木哲郎博士)
【Date & Time】13 March 2008 (Thur), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Tetsuro Suzuki(鈴木哲郎博士)
【Affiliation】Particle Simulation & Thermodynamics group, NIMS-CMSC(NIMS-CMSC 粒子・統計熱力学G)
【Title】Role of randomness in martensitic transformation
乱雑性のマルテンサイト変態における役割
【Abstract】
Critical role of randomness in the martensitic transformation is examined by use of molecular dynamics and random field Ising spin model (RFIM). Sarkar, Ren and Otsuka have recently reported that the usual abrupt onset of the martensitic transformation in Ti-Ni alloy is replaced by the continuous one by introducing deviation from 50-50 stoichiometry. We have shown by molecular dynamics that this is caused by the randomness associated the deviation from the stoichiometry. RFIM shows that such replacement of abrupt onset by continuous one as reported above is one example of the critical role of randomness in a wide range of first order phase transition.
乱雑性のマルテンサイト変態における役割を、分子動力学法と“乱雑場におけるイジングスピンモデル”(RFIM) を用いて調べた。Sarkar, Ren and Otsukaは最近、Ti-Ni合金における通常のはっきりした開始温度を示すマルテンサイト変態が、50:50の化学量論組成からのずれを導入するに伴って連続的な変態に移行することを報告した。我々は分子動力学法により、この不連続的変態から連続的変態の移行は、化学量論組成からのずれの導入に伴う乱雑性によるものと考えられる事を示した。RFIMは、このような不連続的変態から連続的変態への移行は広い範囲の一次相変態における乱雑性の重要な役割の一例である事を示している。
【Contact】Dr. Masato Shimono(下野昌人）
【Place】6F seminar room, Sengen site
【Speaker】Dr. Tetsuro Suzuki(鈴木哲郎博士)
【Affiliation】Particle Simulation & Thermodynamics group, NIMS-CMSC(NIMS-CMSC 粒子・統計熱力学G)
【Title】Role of randomness in martensitic transformation
乱雑性のマルテンサイト変態における役割
【Abstract】
Critical role of randomness in the martensitic transformation is examined by use of molecular dynamics and random field Ising spin model (RFIM). Sarkar, Ren and Otsuka have recently reported that the usual abrupt onset of the martensitic transformation in Ti-Ni alloy is replaced by the continuous one by introducing deviation from 50-50 stoichiometry. We have shown by molecular dynamics that this is caused by the randomness associated the deviation from the stoichiometry. RFIM shows that such replacement of abrupt onset by continuous one as reported above is one example of the critical role of randomness in a wide range of first order phase transition.
乱雑性のマルテンサイト変態における役割を、分子動力学法と“乱雑場におけるイジングスピンモデル”(RFIM) を用いて調べた。Sarkar, Ren and Otsukaは最近、Ti-Ni合金における通常のはっきりした開始温度を示すマルテンサイト変態が、50:50の化学量論組成からのずれを導入するに伴って連続的な変態に移行することを報告した。我々は分子動力学法により、この不連続的変態から連続的変態の移行は、化学量論組成からのずれの導入に伴う乱雑性によるものと考えられる事を示した。RFIMは、このような不連続的変態から連続的変態への移行は広い範囲の一次相変態における乱雑性の重要な役割の一例である事を示している。
【Contact】Dr. Masato Shimono(下野昌人）
Modeling of Materials Deformation - First Principle Study of Ductility of Solids -
材料の変形のモデリング
Prof. Shigenobu Ogata(尾方成信教授)
【Date & Time】6 March 2008 (Thur), 1:30 pm - 3:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Prof. Shigenobu Ogata(尾方成信教授)
【Affiliation】Department of Mechanical Science and Bioengineering, Osaka University(大阪大学大学院基礎工学研究科機能創成専攻)
【Title】Modeling of Materials Deformation - First Principle Study of Ductility of Solids -
材料の変形のモデリング
【Abstract】
We newly propose ductility parameter D, which is defined as the ratio of energies needed for bond breaking under uniform shear and tensile deformations. So far the ratio of bulk modulus and shear modulus [1] and ideal tensile and shear strength [2] and so on are carried out to estimate ductility of solids. However they cannot clearly demonstrate the actual big ductility gap between ceramics and metals. We estimated our proposed D of 23 materials including different ceramics, alloys and metals by performing shear and tensile testing simulations to these materials using ab-initio density functional theory method [3]. We find that (1) ductility of crystalline solids is mainly controlled by the ideal shear strain [4], (2) the D can clearly demonstrate the big ductility gap between ceramics and metals, and (3) the D has clear linear correlation with widely used experimental toughness value in wide range of different materials from ceramics to metals. Hence we conclude D is a good predictor of ductility and also fracture toughness.
[1] A. Kelly, W. R. Tyson and A. H. Cottrell, Philos. Mag., Vol. 15 (1967), p. 567.
[2] S. S. Hecker, D. L. Rohr and D. F. Stein, Met. Trans., Vol. A 9 (1978), p. 481.
[3] G. Kresse and J. Furthmuller, Phys. Rev. B, Vol. 54 (1996), p. 11169.
[4] S. Ogata, J. Li, N. Hirosaki, Y. Shibutani and S. Yip, Phys. Rev. B, Vol. 70 (2004), 104104.
【Contact】Dr. Taichi Abe(阿部太一）
【Place】6F seminar room, Sengen site
【Speaker】Prof. Shigenobu Ogata(尾方成信教授)
【Affiliation】Department of Mechanical Science and Bioengineering, Osaka University(大阪大学大学院基礎工学研究科機能創成専攻)
【Title】Modeling of Materials Deformation - First Principle Study of Ductility of Solids -
材料の変形のモデリング
【Abstract】
We newly propose ductility parameter D, which is defined as the ratio of energies needed for bond breaking under uniform shear and tensile deformations. So far the ratio of bulk modulus and shear modulus [1] and ideal tensile and shear strength [2] and so on are carried out to estimate ductility of solids. However they cannot clearly demonstrate the actual big ductility gap between ceramics and metals. We estimated our proposed D of 23 materials including different ceramics, alloys and metals by performing shear and tensile testing simulations to these materials using ab-initio density functional theory method [3]. We find that (1) ductility of crystalline solids is mainly controlled by the ideal shear strain [4], (2) the D can clearly demonstrate the big ductility gap between ceramics and metals, and (3) the D has clear linear correlation with widely used experimental toughness value in wide range of different materials from ceramics to metals. Hence we conclude D is a good predictor of ductility and also fracture toughness.
[1] A. Kelly, W. R. Tyson and A. H. Cottrell, Philos. Mag., Vol. 15 (1967), p. 567.
[2] S. S. Hecker, D. L. Rohr and D. F. Stein, Met. Trans., Vol. A 9 (1978), p. 481.
[3] G. Kresse and J. Furthmuller, Phys. Rev. B, Vol. 54 (1996), p. 11169.
[4] S. Ogata, J. Li, N. Hirosaki, Y. Shibutani and S. Yip, Phys. Rev. B, Vol. 70 (2004), 104104.
【Contact】Dr. Taichi Abe(阿部太一）
First-principles study of 5H-BN and related polytypes
5H-BN及び関連化合物(polytypes)の第一原理計算
Dr. Kazuaki Kobayashi(小林一昭博士)
【Date & Time】21 February 2008 (Thur), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Kazuaki Kobayashi(小林一昭博士)
【Affiliation】First-Principles Simulation group (II), NIMS-CMSC(NIMS-CMSC 第一原理反応G)
【Title】First-principles study of 5H-BN and related polytypes
5H-BN及び関連化合物(polytypes)の第一原理計算
【Abstract】
5H-BN has been synthesized by Komatsu et al.[1] 5H-BN is one of polytypes which are sp3 bonded hexagonal layered compounds. We have calculated the electronic and lattice properties of BN,[2] SiC, and AlN polytypes. Calculated polytypes are 2H, 3C(=3H), 4H, 5H, and 6H. We have found that 6H-AlN(ABCBCB) is more favorable than 6H-AlN(ABCACB) [Kobayashi and S. Komatsu: submitted to JPSJ]. This seminar will be talked in Japanese. Some slides are edited in Japanese for JSAP Spring meeting.
[1] S. Komatsu, K. Okada, Y. Shimizu, and Y. Moriyoshi: J. Phys. Chem. B 103 (1999) 3289.
[2] K. Kobayashi and S. Komatsu: J. Phys. Soc. Jpn. 76 (2007) 113707.
5H-BNは小松等によってレーザー・プラズマプロセスを使って合成された新しいsp3結合性六方晶層状窒化ホウ素である[1]。その結晶対称性はP3m1、hexagonalityは40%、Zhdanovnotationは(41)である。5H-BN[2]及び関連化合物の第一原理計算を行った結果について話す。特に6H-AlNではP3m1 対称性を持った構造の全エネルギーが、P63mc 対称性を持ったものより低くなることが分かった（Kobayashi and S. Komatsu: JPSJに投稿中）。尚、本講演は日本語で行われる。スライドの一部は2008年応物学会春季講演会のため日本語である。
【Contact】Dr. Masao Arai (新井正男)
【Place】6F seminar room, Sengen site
【Speaker】Dr. Kazuaki Kobayashi(小林一昭博士)
【Affiliation】First-Principles Simulation group (II), NIMS-CMSC(NIMS-CMSC 第一原理反応G)
【Title】First-principles study of 5H-BN and related polytypes
5H-BN及び関連化合物(polytypes)の第一原理計算
【Abstract】
5H-BN has been synthesized by Komatsu et al.[1] 5H-BN is one of polytypes which are sp3 bonded hexagonal layered compounds. We have calculated the electronic and lattice properties of BN,[2] SiC, and AlN polytypes. Calculated polytypes are 2H, 3C(=3H), 4H, 5H, and 6H. We have found that 6H-AlN(ABCBCB) is more favorable than 6H-AlN(ABCACB) [Kobayashi and S. Komatsu: submitted to JPSJ]. This seminar will be talked in Japanese. Some slides are edited in Japanese for JSAP Spring meeting.
[1] S. Komatsu, K. Okada, Y. Shimizu, and Y. Moriyoshi: J. Phys. Chem. B 103 (1999) 3289.
[2] K. Kobayashi and S. Komatsu: J. Phys. Soc. Jpn. 76 (2007) 113707.
5H-BNは小松等によってレーザー・プラズマプロセスを使って合成された新しいsp3結合性六方晶層状窒化ホウ素である[1]。その結晶対称性はP3m1、hexagonalityは40%、Zhdanovnotationは(41)である。5H-BN[2]及び関連化合物の第一原理計算を行った結果について話す。特に6H-AlNではP3m1 対称性を持った構造の全エネルギーが、P63mc 対称性を持ったものより低くなることが分かった（Kobayashi and S. Komatsu: JPSJに投稿中）。尚、本講演は日本語で行われる。スライドの一部は2008年応物学会春季講演会のため日本語である。
【Contact】Dr. Masao Arai (新井正男)
Towards chemical accuracy for molecular processes on oxide surfaces
Prof. M. J. Gillan
【Date & Time】4 February 2008 (Mon), 3:30 pm - 5:00 pm
【Place】8F larger seminar room, Sengen site
【Speaker】Prof. M. J. Gillan
【Affiliation】Materials Simulation Laboragtory, London Centre for Nanotechnology, Department of Physics and Astronomy, University College London, UK
【Title】Towards chemical accuracy for molecular processes on oxide surfaces
【Abstract】
Density functional theory (DFT) is widely used for studying the energetics of molecular processes on surfaces, but for oxide surfaces its accuracy leaves much to be desired. For example, the adsorption energy of the H2O molecule on the MgO (001) surface calculated with different exchange-correlation functionals varies by over 0.5 eV. It is clear that DFT calculations for such systems need to be calibrated against more systematic and accurate methods, which should themselves be checked against experimental measurements. Taking H2O on MgO (001) as an example, I will show how both quantum Monte Carlo (QMC) calculations and high-level quantum chemistry methods can be used to place constraints on the errors of DFT calculations. I will also outline how statistical-mechanical calculations of the absolute molecular desorption rate, compared with the results of temperature programmed desorption experiments, can provide another way of assessing DFT errors. The future possibility of statistical-mechanical calculations based on QMC or high-level quantum chemistry will be indicated.
【Contact】Dr. Tsuyoshi Miyazaki (宮崎剛)
【Place】8F larger seminar room, Sengen site
【Speaker】Prof. M. J. Gillan
【Affiliation】Materials Simulation Laboragtory, London Centre for Nanotechnology, Department of Physics and Astronomy, University College London, UK
【Title】Towards chemical accuracy for molecular processes on oxide surfaces
【Abstract】
Density functional theory (DFT) is widely used for studying the energetics of molecular processes on surfaces, but for oxide surfaces its accuracy leaves much to be desired. For example, the adsorption energy of the H2O molecule on the MgO (001) surface calculated with different exchange-correlation functionals varies by over 0.5 eV. It is clear that DFT calculations for such systems need to be calibrated against more systematic and accurate methods, which should themselves be checked against experimental measurements. Taking H2O on MgO (001) as an example, I will show how both quantum Monte Carlo (QMC) calculations and high-level quantum chemistry methods can be used to place constraints on the errors of DFT calculations. I will also outline how statistical-mechanical calculations of the absolute molecular desorption rate, compared with the results of temperature programmed desorption experiments, can provide another way of assessing DFT errors. The future possibility of statistical-mechanical calculations based on QMC or high-level quantum chemistry will be indicated.
【Contact】Dr. Tsuyoshi Miyazaki (宮崎剛)