CMSセミナー2005
Molecular Dynamics Simulation for Metallic Glasses
金属ガラスに関するMDシミュレーション
Dr. Masato Shimono(下野昌人博士)
【Date & Time】21 December 2005 (Wed), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Masato Shimono(下野昌人博士)
【Affiliation】Particle Simulation & Thermodynamics group, NIMS-CMSC (NIMS-CMSC 粒子・統計熱力学グループ)
【Title】Molecular Dynamics Simulation for Metallic Glasses
金属ガラスに関するMDシミュレーション
【Abstract】
合金の組み合わせを工夫することで実現される金属のガラス状態は、通常の結晶状態とは異なる電磁気・機械的特性を示すため、新しい材料として注目されている。しかしながら、そのガラス化の機構はもとより、ガラス状態の構造すらよく判っていないのが現状である。その点、分子動力学(MD)法は個々の原子の動きを追跡するシミュレーションであり、金属ガラスの構造や物性の解明に適した手法と言える。ただ、計算機の能力から来る制約があるため、極めて短時間のシミュレーションしか出来ない(高々マイクロ秒)という難点がある。そういった制約の下で、合金のガラス形成能の評価をMD法により試みた例を紹介する。
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】6F seminar room, Sengen site
【Speaker】Dr. Masato Shimono(下野昌人博士)
【Affiliation】Particle Simulation & Thermodynamics group, NIMS-CMSC (NIMS-CMSC 粒子・統計熱力学グループ)
【Title】Molecular Dynamics Simulation for Metallic Glasses
金属ガラスに関するMDシミュレーション
【Abstract】
合金の組み合わせを工夫することで実現される金属のガラス状態は、通常の結晶状態とは異なる電磁気・機械的特性を示すため、新しい材料として注目されている。しかしながら、そのガラス化の機構はもとより、ガラス状態の構造すらよく判っていないのが現状である。その点、分子動力学(MD)法は個々の原子の動きを追跡するシミュレーションであり、金属ガラスの構造や物性の解明に適した手法と言える。ただ、計算機の能力から来る制約があるため、極めて短時間のシミュレーションしか出来ない(高々マイクロ秒)という難点がある。そういった制約の下で、合金のガラス形成能の評価をMD法により試みた例を紹介する。
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Ab initio molecular dynamics simulation of molecular radicals in solution
Prof. Michiel Sprik
【Date & Time】16 November 2005 (Wed), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Professor Michiel Sprik
【Affiliation】Department of Chemistry, University of Cambridge
【Title】Ab initio molecular dynamics simulation of molecular radicals in solution
【Abstract】
Radical species in solution are of interest because of their high chemical reactivity. The theoretical description of the solvation of radicals is therefore a suitable topic for all-atom density functional methods. It is also a challenge because some of these methods, in particular the density functionals used in ab initio molecular dynamics simulation ("Car-Parrinello") tend to overestimate the reactivity which may go as as far as the radical wrongly attacking the solvent. In this talk we present some of our recent work in this area, Systems we have studied (in collaboration with others) include the hydroxyl (OH), peroxyl (O$_2$H), superoxide (O$_2^-$) and vitamin C radicals in water and also molecular ions (TTF, TH, quinones) in non-aqueous solvents (acetonitril, methanol). We will focus on the solvation and structure of the unpaired electron (or hole).
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】6F seminar room, Sengen site
【Speaker】Professor Michiel Sprik
【Affiliation】Department of Chemistry, University of Cambridge
【Title】Ab initio molecular dynamics simulation of molecular radicals in solution
【Abstract】
Radical species in solution are of interest because of their high chemical reactivity. The theoretical description of the solvation of radicals is therefore a suitable topic for all-atom density functional methods. It is also a challenge because some of these methods, in particular the density functionals used in ab initio molecular dynamics simulation ("Car-Parrinello") tend to overestimate the reactivity which may go as as far as the radical wrongly attacking the solvent. In this talk we present some of our recent work in this area, Systems we have studied (in collaboration with others) include the hydroxyl (OH), peroxyl (O$_2$H), superoxide (O$_2^-$) and vitamin C radicals in water and also molecular ions (TTF, TH, quinones) in non-aqueous solvents (acetonitril, methanol). We will focus on the solvation and structure of the unpaired electron (or hole).
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Quantum Monte Carlo methods for the surface chemistry of oxide materials
Prof. M. J. Gillan
【Date & Time】9 November 2005 (Wed), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Professor M. J. Gillan
【Affiliation】Physics and Astronomy Department and London Centre for Nanotechnology, University College London
【Title】Quantum Monte Carlo methods for the surface chemistry of oxide materials
【Abstract】
Oxide materials are important for many reasons: catalysis, corrosion, gas-sensing, coatings, etc... Density functional theory (DFT) has been used for nearly 15 years to study the energetics and structure of oxide surfaces, and the adsorption and reactions of molecules on these surfaces. However, it has become clear over the past five years that the usual DFT methods are not very accurate or reliable. For example, the adsorption energies of molecules are often in error by up to 0.5 eV (up to 10 kcal/mol). This poor accuracy is not good enough for many practical purposes. This seminar will describe our recent efforts at UCL to apply quantum Monte Carlo techniques (QMC) to these problems. The basic ideas of QMC will be summarised, and examples of their use for small molecules will be shown. Some recent technical developments in basis sets for QMC will then be outlined. Then, the results of our recent QMC calculations on the prototype oxide MgO will be presented, and I will also present our encouraging results on the MgO (001) surface. Finally, I plan to mention preliminary QMC work on the adsorption of the water molecule on the MgO (001) surface.
【Contact】Dr. Tsuyoshi Miyazaki (宮崎剛)
【Place】6F seminar room, Sengen site
【Speaker】Professor M. J. Gillan
【Affiliation】Physics and Astronomy Department and London Centre for Nanotechnology, University College London
【Title】Quantum Monte Carlo methods for the surface chemistry of oxide materials
【Abstract】
Oxide materials are important for many reasons: catalysis, corrosion, gas-sensing, coatings, etc... Density functional theory (DFT) has been used for nearly 15 years to study the energetics and structure of oxide surfaces, and the adsorption and reactions of molecules on these surfaces. However, it has become clear over the past five years that the usual DFT methods are not very accurate or reliable. For example, the adsorption energies of molecules are often in error by up to 0.5 eV (up to 10 kcal/mol). This poor accuracy is not good enough for many practical purposes. This seminar will describe our recent efforts at UCL to apply quantum Monte Carlo techniques (QMC) to these problems. The basic ideas of QMC will be summarised, and examples of their use for small molecules will be shown. Some recent technical developments in basis sets for QMC will then be outlined. Then, the results of our recent QMC calculations on the prototype oxide MgO will be presented, and I will also present our encouraging results on the MgO (001) surface. Finally, I plan to mention preliminary QMC work on the adsorption of the water molecule on the MgO (001) surface.
【Contact】Dr. Tsuyoshi Miyazaki (宮崎剛)
ntroduction to the NMTO method: Direct generation of Wannier functions and its applications
Dr. Atsushi Yamasaki (山崎敦嗣博士)
【Date & Time】25 October 2005 (Tue), 10:30 am - 12:00 am
【Place】6F seminar room, Sengen site
【Speaker】Dr. Atsushi Yamasaki (山崎敦嗣博士)
【Affiliation】Max-Planck-Institut fuer Festkperforschung, Stuttgart
【Title】ntroduction to the NMTO method: Direct generation of Wannier functions and its applications
【Abstract】
Recently new generation of the LMTO method is developing, so-called NMTO, Nth-order muffin-tin orbital. The keywords, which is nearly connected with each other, are as follows: (1)minimal basis set (by massive downfolding) (2)short-ranged orbitals (by screening transformations) (3)accurate and robust (by overlapping MT-potentials and a polynomial approximation to the energy dependence of the partial-wave set) Those are explained briefly. With the massive downfolding and energy-selective partial waves, it is possible to generate Wannier functions directly, instead of via projection from the delocalized Bloch states. NMTO Wannier functions can be used to visualize chemical bonding and to construct effective (Hubbard-type) Hamiltonians, which are including chemical trends and material dependencies correctly, for strongly correlated systems. The results of the series of 3d(t$_{2g}$)$^1$ perovskites by means of LDA+DMFT are presented. If time permits, other results are also given. These MTO's have significant advantages over those used in the past.
【Contact】Dr. Igor Solovyev
【Place】6F seminar room, Sengen site
【Speaker】Dr. Atsushi Yamasaki (山崎敦嗣博士)
【Affiliation】Max-Planck-Institut fuer Festkperforschung, Stuttgart
【Title】ntroduction to the NMTO method: Direct generation of Wannier functions and its applications
【Abstract】
Recently new generation of the LMTO method is developing, so-called NMTO, Nth-order muffin-tin orbital. The keywords, which is nearly connected with each other, are as follows: (1)minimal basis set (by massive downfolding) (2)short-ranged orbitals (by screening transformations) (3)accurate and robust (by overlapping MT-potentials and a polynomial approximation to the energy dependence of the partial-wave set) Those are explained briefly. With the massive downfolding and energy-selective partial waves, it is possible to generate Wannier functions directly, instead of via projection from the delocalized Bloch states. NMTO Wannier functions can be used to visualize chemical bonding and to construct effective (Hubbard-type) Hamiltonians, which are including chemical trends and material dependencies correctly, for strongly correlated systems. The results of the series of 3d(t$_{2g}$)$^1$ perovskites by means of LDA+DMFT are presented. If time permits, other results are also given. These MTO's have significant advantages over those used in the past.
【Contact】Dr. Igor Solovyev
Interpretation of Hund's multiplicity rule / フント第一則の解釈に関する研究
Dr. Ryo Maezono(前園涼博士)
【Date & Time】12 October 2005 (Wed), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Ryo Maezono(前園涼博士)
【Affiliation】First-Principles Simulation group (II), NIMS-CMSC (NIMS-CMSC 第一原理反応G)
【Title】Interpretation of Hund's multiplicity rule / フント第一則の解釈に関する研究
【Abstract】
Hund's multiplicity rule is investigated for atomic systems using quantum Monte Carlo methods. Our calculations give an accurate account of electronic correlation and obey the virial theorem to high accuracy. This allows us to obtain accurate values for each of the energy terms and therefore to give a convincing explanation of the mechanism. We find that the energy gain in high spin states with respect to low spin states is due to the greater electron-nucleus attraction in the higher spin state, in accordance with Hartree-Fock calculations and studies including correlation.
フントの第一規則は、「原子の基底状態において最も高いスピン多重度 状態が実現される」という広く知られている経験法則であるが其の成因 については、通常、「多電子系が互いにスピンの向きを揃えることに よって会合を避け、電子間相互作用の損をなるべく小さくする」事によ り実現されていると説明されることが多い。一方、精密な量子化学計算 を行うと、スピンの向きを揃えた基底状態の方が電子間相互作用の損が 大きくなることが以前から指摘されていた。本講演では、この問題につ いての歴史的経緯や、最近の講演者らによる量子拡散モンテカルロ計算 を用いた検証計算を詳解する。また此の手法に関する概要も述べる。
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】6F seminar room, Sengen site
【Speaker】Dr. Ryo Maezono(前園涼博士)
【Affiliation】First-Principles Simulation group (II), NIMS-CMSC (NIMS-CMSC 第一原理反応G)
【Title】Interpretation of Hund's multiplicity rule / フント第一則の解釈に関する研究
【Abstract】
Hund's multiplicity rule is investigated for atomic systems using quantum Monte Carlo methods. Our calculations give an accurate account of electronic correlation and obey the virial theorem to high accuracy. This allows us to obtain accurate values for each of the energy terms and therefore to give a convincing explanation of the mechanism. We find that the energy gain in high spin states with respect to low spin states is due to the greater electron-nucleus attraction in the higher spin state, in accordance with Hartree-Fock calculations and studies including correlation.
フントの第一規則は、「原子の基底状態において最も高いスピン多重度 状態が実現される」という広く知られている経験法則であるが其の成因 については、通常、「多電子系が互いにスピンの向きを揃えることに よって会合を避け、電子間相互作用の損をなるべく小さくする」事によ り実現されていると説明されることが多い。一方、精密な量子化学計算 を行うと、スピンの向きを揃えた基底状態の方が電子間相互作用の損が 大きくなることが以前から指摘されていた。本講演では、この問題につ いての歴史的経緯や、最近の講演者らによる量子拡散モンテカルロ計算 を用いた検証計算を詳解する。また此の手法に関する概要も述べる。
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
New density-functional (DF) MD methods for redox (electron-transfer) reactions
酸化還元（電子移動）反応解析のための新しい第一原理分子動力学手法
Dr. Yoshitaka Tateyama (館山佳尚博士)
【Date & Time】6 October 2005 (Thu), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Yoshitaka Tateyama (館山佳尚博士)
【Affiliation】First-Principles Simulation group (I), NIMS-CMSC (NIMS-CMSC 第一原理物性G)
【Title】New density-functional (DF) MD methods for redox (electron-transfer) reactions
酸化還元（電子移動）反応解析のための新しい第一原理分子動力学手法
【Abstract】
Redox (electron transfer) reaction in solution is a vital process in many interesting phenomena such as corrosion, battery, fuel cell, catalysis, photosynthesis. However, few ab-initio methods can compute the key properties of redox reactions. We have developed new theoretical approaches, 'grand-canonical DF-MD' and 'DF-MD+energy gap formula' methods, for quantitative calculation of such quantities. Besides, we demonstrated the validity of these two approaches by using model redox reactions of transition-metal complexes in aqueous solution. In this talk, the methodology, physical implication and typical accuracy will be presented.
酸化還元反応は多くの興味深い現象ー腐食、（燃料）電池、触媒、光合成などーの重要な素過程となっている。しかし酸化還元反応の諸物理量ー酸化還元電位などーを第一原理的に計算する手法は今までなかった。この問題に対し、我々は最近２つの新しい第一原理分子動力学手法ー「grand-canonical DF-MD」及び「DF-MD + Marcus energy gap law」ーを開発し、その有効性を確認した。本講演ではその手法論及び水溶液中の遷移金属錯体系を用いた精度検証について報告する。
【Contact】Dr. Taizo Sasaki (佐々木泰造)
【Place】6F seminar room, Sengen site
【Speaker】Dr. Yoshitaka Tateyama (館山佳尚博士)
【Affiliation】First-Principles Simulation group (I), NIMS-CMSC (NIMS-CMSC 第一原理物性G)
【Title】New density-functional (DF) MD methods for redox (electron-transfer) reactions
酸化還元（電子移動）反応解析のための新しい第一原理分子動力学手法
【Abstract】
Redox (electron transfer) reaction in solution is a vital process in many interesting phenomena such as corrosion, battery, fuel cell, catalysis, photosynthesis. However, few ab-initio methods can compute the key properties of redox reactions. We have developed new theoretical approaches, 'grand-canonical DF-MD' and 'DF-MD+energy gap formula' methods, for quantitative calculation of such quantities. Besides, we demonstrated the validity of these two approaches by using model redox reactions of transition-metal complexes in aqueous solution. In this talk, the methodology, physical implication and typical accuracy will be presented.
酸化還元反応は多くの興味深い現象ー腐食、（燃料）電池、触媒、光合成などーの重要な素過程となっている。しかし酸化還元反応の諸物理量ー酸化還元電位などーを第一原理的に計算する手法は今までなかった。この問題に対し、我々は最近２つの新しい第一原理分子動力学手法ー「grand-canonical DF-MD」及び「DF-MD + Marcus energy gap law」ーを開発し、その有効性を確認した。本講演ではその手法論及び水溶液中の遷移金属錯体系を用いた精度検証について報告する。
【Contact】Dr. Taizo Sasaki (佐々木泰造)
All electron calculations in condensed matter: the GAPW approach
Dr. Marcella Iannuzzi
【Date & Time】3 October 2005 (Mon), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Marcella Iannuzzi
【Affiliation】Physical Chemistry Institute, University of Zurich
【Title】All electron calculations in condensed matter: the GAPW approach
【Abstract】
Our recent work focused on the development of methods to perform Kohn--Sham calculations using accurate basis sets on large systems, including condensed matter systems (periodic boundary conditions). The Gaussian Augmented Plane Wave method (GAPW) is a hybrid method that combines the advantages of the plane waves approach with the expansion of the KS orbitals in terms of localized functions, thus achieving significant improvements in accuracy and efficiency. Moreover, it can be extended to all electron calculations, which are mandatory to reproduce with high accuracy those properties, such as magnetic response or the x-ray absorption/emission spectra, which depend critically on the details of the wavefunctions in the core regions. Some results are presented about x-ray spectroscopy simulations for water systems. For the calculation of properties like the excitation energies and the chemical shifts, we reformulated the generalized density functional perturbation theory in terms of the GAPW scheme. Preliminary results are given to demonstrate accuracy and performance of the method.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】6F seminar room, Sengen site
【Speaker】Dr. Marcella Iannuzzi
【Affiliation】Physical Chemistry Institute, University of Zurich
【Title】All electron calculations in condensed matter: the GAPW approach
【Abstract】
Our recent work focused on the development of methods to perform Kohn--Sham calculations using accurate basis sets on large systems, including condensed matter systems (periodic boundary conditions). The Gaussian Augmented Plane Wave method (GAPW) is a hybrid method that combines the advantages of the plane waves approach with the expansion of the KS orbitals in terms of localized functions, thus achieving significant improvements in accuracy and efficiency. Moreover, it can be extended to all electron calculations, which are mandatory to reproduce with high accuracy those properties, such as magnetic response or the x-ray absorption/emission spectra, which depend critically on the details of the wavefunctions in the core regions. Some results are presented about x-ray spectroscopy simulations for water systems. For the calculation of properties like the excitation energies and the chemical shifts, we reformulated the generalized density functional perturbation theory in terms of the GAPW scheme. Preliminary results are given to demonstrate accuracy and performance of the method.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
First Principles Computational Studies of Hydrogen Storage in Pure Mg and in Novel Mg Nanocomposites
Prof. Sean C. Smith
【Date & Time】14 September 2005 (Wed), 10:30 pm - 11:30 pm
【Place】6F seminar room, Sengen site
【Speaker】Professor Sean C. Smith
【Affiliation】Centre for Computational Molecular Science, The University of Queensland
【Title】First Principles Computational Studies of Hydrogen Storage in Pure Mg and in Novel Mg Nanocomposites
【Abstract】
We have recently been intensively involved in first principles computational modelling of hydrogen dissociative chemisorption, diffusion and desorption with pure Mg and Mg-based nanocomposite materials, with a focus on the development of effective hydrogen storage media. A key challenge to be addressed is the integration of catalytic effects for each of these components of the hydrogen storage process within a single, easily manufacturable material. Our calculations utilise density functional theory with the generalised gradient approximation, coupled with the nudged elastic band method for determination of reaction paths and barriers. The computational results assist in the interpretation of experimental hydrogen storage studies for nanocomposites produced by ball-milling.
【Contact】Dr. Hidehiro Onodera (小野寺秀博)
【Place】6F seminar room, Sengen site
【Speaker】Professor Sean C. Smith
【Affiliation】Centre for Computational Molecular Science, The University of Queensland
【Title】First Principles Computational Studies of Hydrogen Storage in Pure Mg and in Novel Mg Nanocomposites
【Abstract】
We have recently been intensively involved in first principles computational modelling of hydrogen dissociative chemisorption, diffusion and desorption with pure Mg and Mg-based nanocomposite materials, with a focus on the development of effective hydrogen storage media. A key challenge to be addressed is the integration of catalytic effects for each of these components of the hydrogen storage process within a single, easily manufacturable material. Our calculations utilise density functional theory with the generalised gradient approximation, coupled with the nudged elastic band method for determination of reaction paths and barriers. The computational results assist in the interpretation of experimental hydrogen storage studies for nanocomposites produced by ball-milling.
【Contact】Dr. Hidehiro Onodera (小野寺秀博)
Computer simulation of grain growth in three dimensions by the phase field model
Phase-fieldモデルによる３次元結晶粒成長の計算機シミュレーション
Dr. Yoshihiro Suwa(諏訪義宏博士)
【Date & Time】21 July 2005 (Thu), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Yoshihiro Suwa(諏訪義宏博士)
【Affiliation】Particle Simulation & Thermodynamics group, NIMS-CMSC (NIMS-CMSC 粒子・統計熱力学G)
【Title】Computer simulation of grain growth in three dimensions by the phase field model
Phase-fieldモデルによる３次元結晶粒成長の計算機シミュレーション
【Abstract】
金属を含む多結晶物質の結晶粒構造は、物性値を決定するカギとなる要素である。構造の幾何学的特徴を粒成長の解析的な理論に直接組み込むことは困難なので、コンピュータシミュレーションを用いることが多くなっており、これまで、Monte Carlo法をはじめとする、様々なモデルが提案されている。近年、計算材料科学の分野で目覚しい発展を遂げているphase-field法を粒成長シミュレーションに適用する試みが行われてきた。 発表では、phase-field法による三次元多結晶成長のシミュレーションについて、その他の手法による結果と比較しながら、正常粒成長、異常粒成長（二次再結晶）の計算結果に加えて、第二相分散粒子が粒成長に与える影響（Zener pinning）について報告する。
【Contact】Dr. Toshiyuki Koyama (小山敏幸)
【Place】6F seminar room, Sengen site
【Speaker】Dr. Yoshihiro Suwa(諏訪義宏博士)
【Affiliation】Particle Simulation & Thermodynamics group, NIMS-CMSC (NIMS-CMSC 粒子・統計熱力学G)
【Title】Computer simulation of grain growth in three dimensions by the phase field model
Phase-fieldモデルによる３次元結晶粒成長の計算機シミュレーション
【Abstract】
金属を含む多結晶物質の結晶粒構造は、物性値を決定するカギとなる要素である。構造の幾何学的特徴を粒成長の解析的な理論に直接組み込むことは困難なので、コンピュータシミュレーションを用いることが多くなっており、これまで、Monte Carlo法をはじめとする、様々なモデルが提案されている。近年、計算材料科学の分野で目覚しい発展を遂げているphase-field法を粒成長シミュレーションに適用する試みが行われてきた。 発表では、phase-field法による三次元多結晶成長のシミュレーションについて、その他の手法による結果と比較しながら、正常粒成長、異常粒成長（二次再結晶）の計算結果に加えて、第二相分散粒子が粒成長に与える影響（Zener pinning）について報告する。
【Contact】Dr. Toshiyuki Koyama (小山敏幸)
Terahertz Emission using High Temperature Superconductors
高温超伝導体を使った連続テラヘルツ波の発振
Prof. Masashi Tachiki(立木昌教授)
【Date & Time】14 July 2005 (Thu), 3:30 pm - 5:00 pm
【Place】8F large seminar room, Sengen site
【Speaker】Professor Masashi Tachiki(立木昌教授)
【Affiliation】NIMS
【Title】Terahertz Emission using High Temperature Superconductors
高温超伝導体を使った連続テラヘルツ波の発振
【Abstract】
The structure of high temperature superconductors comprise stacks of naturally-built Josephson junctions. These junctions sustain a new form of excitation, i.e. Josephson plasmas (falling in the terahertz range) which lie within the superconducting energy gap and is thus protected from Landau damping. If a method of exciting this state can be devised, it will therefore offer a promising way of emitting electromagnetic fields in the Terahertz range. The above scenario can be formulated into a set of nonlinear equations. I present solutions of these equations utilizing the Earth Simulator, and compare them with recent experiments.
高温超伝導体は自然に積み重なったジョセフソン接合体を構成している。その中ではジョセフソンプラズマと呼ばれる新しい励起状態がテラヘルツ周波数領域に存在し、それが超伝導ギャップの中にあるためランダウ・ダンピングを受けにくい。従って何らかの方法でこの状態を励起すると、テラヘルツの電磁波を発振し、減衰することになる。以上の機構を定式化すると非線形連立方程式を得る。これを地球シミュレータで計算して解いた結果と実験との比較をお話ししたい。
【Contact】Dr. Akihiro Tanaka (田中秋広)
【Place】8F large seminar room, Sengen site
【Speaker】Professor Masashi Tachiki(立木昌教授)
【Affiliation】NIMS
【Title】Terahertz Emission using High Temperature Superconductors
高温超伝導体を使った連続テラヘルツ波の発振
【Abstract】
The structure of high temperature superconductors comprise stacks of naturally-built Josephson junctions. These junctions sustain a new form of excitation, i.e. Josephson plasmas (falling in the terahertz range) which lie within the superconducting energy gap and is thus protected from Landau damping. If a method of exciting this state can be devised, it will therefore offer a promising way of emitting electromagnetic fields in the Terahertz range. The above scenario can be formulated into a set of nonlinear equations. I present solutions of these equations utilizing the Earth Simulator, and compare them with recent experiments.
高温超伝導体は自然に積み重なったジョセフソン接合体を構成している。その中ではジョセフソンプラズマと呼ばれる新しい励起状態がテラヘルツ周波数領域に存在し、それが超伝導ギャップの中にあるためランダウ・ダンピングを受けにくい。従って何らかの方法でこの状態を励起すると、テラヘルツの電磁波を発振し、減衰することになる。以上の機構を定式化すると非線形連立方程式を得る。これを地球シミュレータで計算して解いた結果と実験との比較をお話ししたい。
【Contact】Dr. Akihiro Tanaka (田中秋広)
Merging first-principles and model approaches: GW+DMFT
Dr. Ferdi Aryasetiawan
【Date & Time】23 June 2005 (Thu), 3:00 pm - 4:30 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Ferdi Aryasetiawan
【Affiliation】AIST-RICS (産総研計算科学研究部門)
【Title】Merging first-principles and model approaches: GW+DMFT
【Abstract】
First-principles calculations reveal a lot more details about the system than model calculations can hope to do. On the other hand, model approaches are theoretically more sophisticated than first-principles approaches. By combining the GW method, which is a successful first-principles method beyond the LDA, and dynamical mean-field theory (DMFT), which is traditionally applied to study strongly correlated systems in the model context, we obtain a first-principles scheme that incorporates the strength of DMFT in treating systems with strong onsite correlations. The new scheme was tested in ferromagnetic nickel with encouraging results.
【Contact】Dr. Hiori Kino (木野日織)
【Place】6F seminar room, Sengen site
【Speaker】Dr. Ferdi Aryasetiawan
【Affiliation】AIST-RICS (産総研計算科学研究部門)
【Title】Merging first-principles and model approaches: GW+DMFT
【Abstract】
First-principles calculations reveal a lot more details about the system than model calculations can hope to do. On the other hand, model approaches are theoretically more sophisticated than first-principles approaches. By combining the GW method, which is a successful first-principles method beyond the LDA, and dynamical mean-field theory (DMFT), which is traditionally applied to study strongly correlated systems in the model context, we obtain a first-principles scheme that incorporates the strength of DMFT in treating systems with strong onsite correlations. The new scheme was tested in ferromagnetic nickel with encouraging results.
【Contact】Dr. Hiori Kino (木野日織)
Charge localization phenomena in synthetic DNA
Prof. Mauro Boero
【Date & Time】9 June 2005 (Thu), 1:30 pm - 2:30 pm
【Place】6F seminar room, Sengen site
【Speaker】Professor Mauro Boero
【Affiliation】Institute of Physics, University of Tsukuba(筑波大学物理学系)
【Title】Charge localization phenomena in synthetic DNA
【Abstract】
Charge transfer in DNA is currently the subject of intense theoretical and experimental investigation. This is due both to a possible use of DNA as a component in nanoelectronic and electrochemical devices and to the fundamental role of conductivity in the oxidative damage and mutations of DNA. By using Car-Parrinello molecular dynamics, we study the mechanism of positive charge and electron hole localization in a laboratory realizable radical cation Z-DNA crystal[1]. We find that at room temperature structural deformation are not sufficient to provide an efficient localization mechanism. Instead we find evidence for both an ion-gated and proton-coupled mechanism[2]. Namely, a hole h+ can be localized by two mechanisms: (i) proton shift or (ii) fluctuations in the solvation shell[3] (with some warning). Between these two scenarios, the proton-coupled charge transfer mechanism seems to provide the best agreement and the key to interpret EPR and H/D substitution experiments. Due to the large size of the full quantum system, this calculation was performed on the Earth Simulator (ES) computer facility[4]. Work is now in progress on a hybrid QMMM system, coupled to metadynamics, to work out charge localization reaction paths and related activation barriers: few details will be given as closing remarks.
【Contact】Dr. Hiori Kino (木野日織)
【Place】6F seminar room, Sengen site
【Speaker】Professor Mauro Boero
【Affiliation】Institute of Physics, University of Tsukuba(筑波大学物理学系)
【Title】Charge localization phenomena in synthetic DNA
【Abstract】
Charge transfer in DNA is currently the subject of intense theoretical and experimental investigation. This is due both to a possible use of DNA as a component in nanoelectronic and electrochemical devices and to the fundamental role of conductivity in the oxidative damage and mutations of DNA. By using Car-Parrinello molecular dynamics, we study the mechanism of positive charge and electron hole localization in a laboratory realizable radical cation Z-DNA crystal[1]. We find that at room temperature structural deformation are not sufficient to provide an efficient localization mechanism. Instead we find evidence for both an ion-gated and proton-coupled mechanism[2]. Namely, a hole h+ can be localized by two mechanisms: (i) proton shift or (ii) fluctuations in the solvation shell[3] (with some warning). Between these two scenarios, the proton-coupled charge transfer mechanism seems to provide the best agreement and the key to interpret EPR and H/D substitution experiments. Due to the large size of the full quantum system, this calculation was performed on the Earth Simulator (ES) computer facility[4]. Work is now in progress on a hybrid QMMM system, coupled to metadynamics, to work out charge localization reaction paths and related activation barriers: few details will be given as closing remarks.
【Contact】Dr. Hiori Kino (木野日織)
Photonic Anderson Model -Hybridization theory between localized mode and free propagating mode for light scattering from a dielectric sphere-
Dr. Junichi Inoue (井上純一博士)
【Date & Time】2 June 2005 (Thu), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Junichi Inoue (井上純一博士)
【Affiliation】NIMS-ICYS / NIMS nanomaterials lab.
【Title】Photonic Anderson Model -Hybridization theory between localized mode and free propagating mode for light scattering from a dielectric sphere-
【Abstract】
Light scattering from a homogeneous dielectric sphere is discussed in terms of hybridization between a localized mode excited inside the dielectric sphere and free propagating modes in vacuum. This theory is a photonic counterpart of the Anderson model in electron systems, yielding rigorous theoretical foundation of the heavy photon concept, which was numerically proposed for almost flat photonic bands. The magnitude of the hybridization is analytically expressed. The localized mode is identified with the photon virtual bound state. In order to confirm the validity of the present theory, a comparison is made between the present theory and conventional numerical calculation for results of the photonic density of states.
【Contact】Dr. Akihiro Tanaka (田中秋広)
【Place】6F seminar room, Sengen site
【Speaker】Dr. Junichi Inoue (井上純一博士)
【Affiliation】NIMS-ICYS / NIMS nanomaterials lab.
【Title】Photonic Anderson Model -Hybridization theory between localized mode and free propagating mode for light scattering from a dielectric sphere-
【Abstract】
Light scattering from a homogeneous dielectric sphere is discussed in terms of hybridization between a localized mode excited inside the dielectric sphere and free propagating modes in vacuum. This theory is a photonic counterpart of the Anderson model in electron systems, yielding rigorous theoretical foundation of the heavy photon concept, which was numerically proposed for almost flat photonic bands. The magnitude of the hybridization is analytically expressed. The localized mode is identified with the photon virtual bound state. In order to confirm the validity of the present theory, a comparison is made between the present theory and conventional numerical calculation for results of the photonic density of states.
【Contact】Dr. Akihiro Tanaka (田中秋広)
Correlated Electron-Ion Dynamics: quantum molecular dynamics with exchange of energy between ions and electrons
Dr. David Bowler
【Date & Time】26 May 2005 (Thu), 2:30 pm - 4:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. David Bowler
【Affiliation】NIMS-ICYS / Dept. of Physics and Astronomy, University College London
【Title】Correlated Electron-Ion Dynamics: quantum molecular dynamics with exchange of energy between ions and electrons
【Abstract】
Correlated Electron-Ion Dynamics (CEID) is an extension of molecular dynamics that allows us to introduce in a correct manner the exchange of energy between electrons and ions. The formalism is based on a systematic approximation (Small Amplitude Moment Expansion - SAME). I will introduce the formalism and discuss two research directions: implementation with open boundaries, and application to inelastic tunneling spectroscopy. (This work was done in collaboration with A.J.Fisher(UCL), A.P.Horsfield(UCL), C.Sanchez(Queen's Univ. of Belfast) and T.Todorov(Queen's Univ. of Belfast).)
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】6F seminar room, Sengen site
【Speaker】Dr. David Bowler
【Affiliation】NIMS-ICYS / Dept. of Physics and Astronomy, University College London
【Title】Correlated Electron-Ion Dynamics: quantum molecular dynamics with exchange of energy between ions and electrons
【Abstract】
Correlated Electron-Ion Dynamics (CEID) is an extension of molecular dynamics that allows us to introduce in a correct manner the exchange of energy between electrons and ions. The formalism is based on a systematic approximation (Small Amplitude Moment Expansion - SAME). I will introduce the formalism and discuss two research directions: implementation with open boundaries, and application to inelastic tunneling spectroscopy. (This work was done in collaboration with A.J.Fisher(UCL), A.P.Horsfield(UCL), C.Sanchez(Queen's Univ. of Belfast) and T.Todorov(Queen's Univ. of Belfast).)
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
Construction of low-energy effective Hamiltonians using Wannier functions formalism
Dr. Igor Solovyev
【Date & Time】18 May 2005 (Wed), 4:00 pm - 5:30 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Igor Solovyev
【Affiliation】First-Principles Simulation group (II), NIMS-CMSC (NIMS-CMSC 第一原理反応G)
【Title】Construction of low-energy effective Hamiltonians using Wannier functions formalism
【Abstract】
There is a large class of compounds whose electronic properties are predetermined by the behavior of a limited number of bands located near the Fermi level and well isolated from the rest of the states, and those electronic structure cannot be described properly using conventional methods based on the local-density approximation (LDA). Several typical examples are the perovskites (SrVO$_3$, LaTiO$_3$, etc.), V$_2$O$_3$, Y$_2$Mo$_2$O$_7$, NaCoO$_2$, and many others. The source of the problem is known to be the on-site Coulomb correlations, whose form is greatly oversimplified in LDA. Therefore, many attempts have been done in order to incorporate the physics of on-site Coulomb correlations in LDA. I will discuss the systematic procedure for constructing the effective low-energy Hubbard-type Hamiltonian for these systems using results of first-principle calculations. This procedure consists of three parts: (1) The derivation of the kinetic-energy part using the downfolding method. (2) Construction of Wannier functions. (3) Calculation of screened Coulomb interactions in the basis of Wannier functions. I will also show applications for transition-metal oxides.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)
【Place】6F seminar room, Sengen site
【Speaker】Dr. Igor Solovyev
【Affiliation】First-Principles Simulation group (II), NIMS-CMSC (NIMS-CMSC 第一原理反応G)
【Title】Construction of low-energy effective Hamiltonians using Wannier functions formalism
【Abstract】
There is a large class of compounds whose electronic properties are predetermined by the behavior of a limited number of bands located near the Fermi level and well isolated from the rest of the states, and those electronic structure cannot be described properly using conventional methods based on the local-density approximation (LDA). Several typical examples are the perovskites (SrVO$_3$, LaTiO$_3$, etc.), V$_2$O$_3$, Y$_2$Mo$_2$O$_7$, NaCoO$_2$, and many others. The source of the problem is known to be the on-site Coulomb correlations, whose form is greatly oversimplified in LDA. Therefore, many attempts have been done in order to incorporate the physics of on-site Coulomb correlations in LDA. I will discuss the systematic procedure for constructing the effective low-energy Hubbard-type Hamiltonian for these systems using results of first-principle calculations. This procedure consists of three parts: (1) The derivation of the kinetic-energy part using the downfolding method. (2) Construction of Wannier functions. (3) Calculation of screened Coulomb interactions in the basis of Wannier functions. I will also show applications for transition-metal oxides.
【Contact】Dr. Yoshitaka Tateyama(館山佳尚)