CMS seminar2009
Fragment MO Molecular Dynamics (FMO-MD)
Dr. Yuto Komeiji
【Date & Time】17 November 2009 (Tue), 13:30 am - 15:00 am
【Place】6F seminar room, Central Bldg., Sengen site
【Speaker】Dr. Yuto Komeiji
【Affiliation】AIST & Rikkyo Univ.
【Title】Fragment MO Molecular Dynamics (FMO-MD)
【Abstract】
The fragment molecular orbital method (Fragment molecular orbital method, FMO) published by Kitaura et al. in 1999 has been developed as a method to calculate the electronic states of macromolecular systems. In 2003, a molecular dynamics method using the FMO method and the FMO-MD method were also developed, and recently applied calculations have been made for low molecular weight compounds in aqueous solutions. In this seminar, we would like to introduce various aspects of FMO-MD, focusing on the following.
・Principle and calculation example of FMO method (electronic state of protein in aqueous solution)
・Principle and program of FMO-MD method (PEACH/ABINIT-MPX system, Blue Moon method)
・Application of FMO-MD Method (Simulation of SN2 Reaction)
・Improvement of FMO-MD method (introduction of three-body effect and general automatic division algorithm)
【Contact】Dr. Hiori Kino
【Place】6F seminar room, Central Bldg., Sengen site
【Speaker】Dr. Yuto Komeiji
【Affiliation】AIST & Rikkyo Univ.
【Title】Fragment MO Molecular Dynamics (FMO-MD)
【Abstract】
The fragment molecular orbital method (Fragment molecular orbital method, FMO) published by Kitaura et al. in 1999 has been developed as a method to calculate the electronic states of macromolecular systems. In 2003, a molecular dynamics method using the FMO method and the FMO-MD method were also developed, and recently applied calculations have been made for low molecular weight compounds in aqueous solutions. In this seminar, we would like to introduce various aspects of FMO-MD, focusing on the following.
・Principle and calculation example of FMO method (electronic state of protein in aqueous solution)
・Principle and program of FMO-MD method (PEACH/ABINIT-MPX system, Blue Moon method)
・Application of FMO-MD Method (Simulation of SN2 Reaction)
・Improvement of FMO-MD method (introduction of three-body effect and general automatic division algorithm)
【Contact】Dr. Hiori Kino
Normal-State Spin Dynamics and Temperature-Dependent Spin Resonance Energy in an Optimally Doped Iron Arsenide Superconductor
Dr. Vladimir Hinkov
【Date & Time】7 September 2009 (Mon) 14:30 – 16:00
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Vladimir Hinkov
【Affiliation】Max-Planck-Institute for Solid State Research
【Title】Normal-State Spin Dynamics and Temperature-Dependent Spin Resonance Energy in an Optimally Doped Iron Arsenide Superconductor
【Abstract】
Using inelastic neutron scattering we have studied the spin excitations in optimally doped BaFe(1.85)Co(0.15)As(2) (Tc = 25 K) over a wide range of temperatures and energies. I will contrast our results to findings in cuprates and heavy fermion superconductors, and discuss their implications to theory. In particular, we find that in contrast to cuprates, the spectrum is in good agreement with predictions of the theory of nearly antiferromagnetic metals, without complications arising from a pseudogap or competing incommensurate spin-modulated phases. This simplifies the theoretical treatment, and our data provide the foundation for the development of quantitative theories of magnetically mediated superconductivity in the iron arsenides.
【Contact】Dr. Hiroyuki Yamase
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Vladimir Hinkov
【Affiliation】Max-Planck-Institute for Solid State Research
【Title】Normal-State Spin Dynamics and Temperature-Dependent Spin Resonance Energy in an Optimally Doped Iron Arsenide Superconductor
【Abstract】
Using inelastic neutron scattering we have studied the spin excitations in optimally doped BaFe(1.85)Co(0.15)As(2) (Tc = 25 K) over a wide range of temperatures and energies. I will contrast our results to findings in cuprates and heavy fermion superconductors, and discuss their implications to theory. In particular, we find that in contrast to cuprates, the spectrum is in good agreement with predictions of the theory of nearly antiferromagnetic metals, without complications arising from a pseudogap or competing incommensurate spin-modulated phases. This simplifies the theoretical treatment, and our data provide the foundation for the development of quantitative theories of magnetically mediated superconductivity in the iron arsenides.
【Contact】Dr. Hiroyuki Yamase
Molecular dynamics simulations of hysteresis loops for BaTiO3 ferroelectric thin-film capacitors using the feram code
Dr. Takeshi Nishimatsu
【Date & Time】4 September 2009 (Fri) 15:30 – 17:00
【Place】5F seminar room, Sengen site
【Speaker】Dr. Takeshi Nishimatsu
【Affiliation】Institute for Materials Research, Tohoku University
【Title】Molecular dynamics simulations of hysteresis loops for BaTiO3 ferroelectric thin-film capacitors using the feram code
【Abstract】
Molecular dynamics (MD) simulations of hysteresis loops are performed for bulk and thin-film BaTiO3 using our original MD code, "feram" (http://loto.sf.net/feram/) [1]. "feram" can simulate temperature, thickness, frequency and electrode dependences of ferroelectric properties. We confirmed that the imperfect screening by the electrodes decreases the coercive field as the film thickness decreases in thin-film ferroelectric capacitors, as described in Ref. [2]. We also found that compressive strain arising from epitaxial constraints suppresses the polarization switching, while the inclusion of inhomogeneous strain (i.e. acoustic displacements) eases the switching.
[1] Takeshi Nishimatsu, Umesh V. Waghmare, Yoshiyuki Kawazoe, and David Vanderbilt: Phys. Rev. B 78 (2008) 104104.
[2] M. Dawber, P. Chandra, P. B. Littlewood and J. F. Scott: J. Phys.-Condes. Matter 15 (2003) L393.
【Contact】Dr. Taizo Sasaki
【Place】5F seminar room, Sengen site
【Speaker】Dr. Takeshi Nishimatsu
【Affiliation】Institute for Materials Research, Tohoku University
【Title】Molecular dynamics simulations of hysteresis loops for BaTiO3 ferroelectric thin-film capacitors using the feram code
【Abstract】
Molecular dynamics (MD) simulations of hysteresis loops are performed for bulk and thin-film BaTiO3 using our original MD code, "feram" (http://loto.sf.net/feram/) [1]. "feram" can simulate temperature, thickness, frequency and electrode dependences of ferroelectric properties. We confirmed that the imperfect screening by the electrodes decreases the coercive field as the film thickness decreases in thin-film ferroelectric capacitors, as described in Ref. [2]. We also found that compressive strain arising from epitaxial constraints suppresses the polarization switching, while the inclusion of inhomogeneous strain (i.e. acoustic displacements) eases the switching.
[1] Takeshi Nishimatsu, Umesh V. Waghmare, Yoshiyuki Kawazoe, and David Vanderbilt: Phys. Rev. B 78 (2008) 104104.
[2] M. Dawber, P. Chandra, P. B. Littlewood and J. F. Scott: J. Phys.-Condes. Matter 15 (2003) L393.
【Contact】Dr. Taizo Sasaki
Linear scaling algorithms: introduction, accuracy, and scalable implementation
Dr. Vincent Sacksteder
【Date & Time】16 July 2009 (Thu) 10:30 – 12:00
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Vincent Sacksteder
【Affiliation】Asia Pacific Center for Theoretical Physics, South Korea
【Title】Linear scaling algorithms: introduction, accuracy, and scalable implementation
【Abstract】
This talk introduces the main ideas of linear scaling algorithms, which promise to extend first principles DFT calculations to large numbers of atoms and large parallel supercomputers. Physically speaking they are implementations of the idea callednearsightedness. I argue that linear scaling algorithms can be exponentially accurate even in metals as long as there is some disorder. Lastly I discuss the enormous difference between having a scalable algorithm and having an implementation which scales to the largest supercomputers, and propose development of a general purpose library for linear scaling codes.
【Contact】Dr. Tsuyoshi Miyazaki
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Vincent Sacksteder
【Affiliation】Asia Pacific Center for Theoretical Physics, South Korea
【Title】Linear scaling algorithms: introduction, accuracy, and scalable implementation
【Abstract】
This talk introduces the main ideas of linear scaling algorithms, which promise to extend first principles DFT calculations to large numbers of atoms and large parallel supercomputers. Physically speaking they are implementations of the idea callednearsightedness. I argue that linear scaling algorithms can be exponentially accurate even in metals as long as there is some disorder. Lastly I discuss the enormous difference between having a scalable algorithm and having an implementation which scales to the largest supercomputers, and propose development of a general purpose library for linear scaling codes.
【Contact】Dr. Tsuyoshi Miyazaki
Theory of quantum transport in superconductor/ferromagnet hybrid junctions
Dr. Shin-ichi Hikino
【Date & Time】13 July 2009 (Mon) 15:30 – 17:00
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Shin-ichi Hikino
【Affiliation】Institute for Materials Research, Tohoku University
【Title】Theory of quantum transport in superconductor/ferromagnet hybrid junctions
【Abstract】
In a Josephson junction with a ferromagnet (FM), which is called the ferromagnetic Josephson junction (FJJ), the Cooper pairs penetrate into the FM and have additional momenta due to the exchange energy in the FM. As a result, the phase of the superconducting order parameter shifts by π. The so-called π-state has been studied extensively. However, the magnetic scattering and magnetization dynamics for Cooper pair has not received much attention in the study of FJJs. Moreover, most of studies on the FJJs have been so far focused on the dc Josephson effect. In this talk, I present three topics: (1) Effect of magnetic scattering in a ferromagnetic Josephson junction, (2) AC Josephson current in a ferromagnetic Josephson junction, and (3) Theory of ferromagnetic Josephson resonance.
【Contact】Dr. Hiroyuki Yamase
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Shin-ichi Hikino
【Affiliation】Institute for Materials Research, Tohoku University
【Title】Theory of quantum transport in superconductor/ferromagnet hybrid junctions
【Abstract】
In a Josephson junction with a ferromagnet (FM), which is called the ferromagnetic Josephson junction (FJJ), the Cooper pairs penetrate into the FM and have additional momenta due to the exchange energy in the FM. As a result, the phase of the superconducting order parameter shifts by π. The so-called π-state has been studied extensively. However, the magnetic scattering and magnetization dynamics for Cooper pair has not received much attention in the study of FJJs. Moreover, most of studies on the FJJs have been so far focused on the dc Josephson effect. In this talk, I present three topics: (1) Effect of magnetic scattering in a ferromagnetic Josephson junction, (2) AC Josephson current in a ferromagnetic Josephson junction, and (3) Theory of ferromagnetic Josephson resonance.
【Contact】Dr. Hiroyuki Yamase
Quantum Network Model and its Application to Quantum Transport Phenomenna
Prof. Tomi Ohtsuki
【Date & Time】8 July 2009 (Wed), 15:30-17:00
【Place】4F seminar room, MANA building, Namiki Site
【Speaker】Prof. Tomi Ohtsuki
【Affiliation】Sophia University
【Title】Quantum Network Model and its Application to Quantum Transport Phenomenna
【Abstract】
Quantum network models, which were originally introduced by Chalker and Coddington to explain the quantum Hall effect, have proved capable of describing a wide range of transport phenomena in disordered systems. Here I give a talk on a series of studies for quantum transport phenomena such as the quantum Hall effect and quantum spin Hall effect, and the effect of perfectly conducting channel.
【Contact】Dr. Katsunori Wakabayashi
【Place】4F seminar room, MANA building, Namiki Site
【Speaker】Prof. Tomi Ohtsuki
【Affiliation】Sophia University
【Title】Quantum Network Model and its Application to Quantum Transport Phenomenna
【Abstract】
Quantum network models, which were originally introduced by Chalker and Coddington to explain the quantum Hall effect, have proved capable of describing a wide range of transport phenomena in disordered systems. Here I give a talk on a series of studies for quantum transport phenomena such as the quantum Hall effect and quantum spin Hall effect, and the effect of perfectly conducting channel.
【Contact】Dr. Katsunori Wakabayashi
Recent developments in non-centrosymmetric superconductors
Prof. Manfred Sigrist
【Date & Time】6 July 2009 (Mon), 10:30 – 12:00
【Place】8F large seminar room, Sengen site
【Speaker】Prof. Manfred Sigrist
【Affiliation】Theoretische Physik, ETH Zurich
【Title】Recent developments in non-centrosymmetric superconductors
【Abstract】
The absence of inversion symmetry in a metal influences the electronic spectrum drastically through spin-orbit coupling by spin-splitting of the states. This affects superconductivity in a special way through a novel Cooper pairing symmetry which is non-unitary and has mixed-parity nature. The study of this type of superconductivity has been mainly motivated by the recent discovery of a number of noncentrosymmetric heavy fermion superconductors, such as CePt3 Si, CeRhSi3 or CeIrSi3 . In this talk I will present the basic concepts of non-centrosymmetric superconductivity and explore some experimental implications for the superconducting phase. In particular, properties in high magnetic fields, the electronic states at twin boundaries and surfaces will be discussed.
【Contact】Dr. Katsunori Wakabayashi
【Place】8F large seminar room, Sengen site
【Speaker】Prof. Manfred Sigrist
【Affiliation】Theoretische Physik, ETH Zurich
【Title】Recent developments in non-centrosymmetric superconductors
【Abstract】
The absence of inversion symmetry in a metal influences the electronic spectrum drastically through spin-orbit coupling by spin-splitting of the states. This affects superconductivity in a special way through a novel Cooper pairing symmetry which is non-unitary and has mixed-parity nature. The study of this type of superconductivity has been mainly motivated by the recent discovery of a number of noncentrosymmetric heavy fermion superconductors, such as CePt3 Si, CeRhSi3 or CeIrSi3 . In this talk I will present the basic concepts of non-centrosymmetric superconductivity and explore some experimental implications for the superconducting phase. In particular, properties in high magnetic fields, the electronic states at twin boundaries and surfaces will be discussed.
【Contact】Dr. Katsunori Wakabayashi
Recent Developments in Conquest:Million Atom DFT and Constrained DFT
Dr. David Bowler
【Date & Time】29 June (Mon) 15:30 - 17:00
【Place】8F large seminar room, SENGEN site
【Speaker】Dr. David Bowler
【Affiliation】Department of Physics & Astronomy, University College London (UCL)
【Title】Recent Developments in Conquest:Million Atom DFT and Constrained DFT
【Abstract】
I will give a description of the linear scaling DFT code Conquest, which has been developed at UCL and NIMS. In particular, I will present recent results on the scaling of the code, and show that it scales perfectly to over 4,000 cores and 2,000,000 atoms on modern high-performance computers. This demonstrates the potential of DFT to address systems of millions of atoms.
I will also discuss the implementation of constrained DFT within the code, and give details of how this method can be used to calculate charge transfer and excitation properties of systems using DFT. I will discuss plans for the application and development of Conquest.
【Contact】Dr. Yoshitaka Tateyama
【Place】8F large seminar room, SENGEN site
【Speaker】Dr. David Bowler
【Affiliation】Department of Physics & Astronomy, University College London (UCL)
【Title】Recent Developments in Conquest:Million Atom DFT and Constrained DFT
【Abstract】
I will give a description of the linear scaling DFT code Conquest, which has been developed at UCL and NIMS. In particular, I will present recent results on the scaling of the code, and show that it scales perfectly to over 4,000 cores and 2,000,000 atoms on modern high-performance computers. This demonstrates the potential of DFT to address systems of millions of atoms.
I will also discuss the implementation of constrained DFT within the code, and give details of how this method can be used to calculate charge transfer and excitation properties of systems using DFT. I will discuss plans for the application and development of Conquest.
【Contact】Dr. Yoshitaka Tateyama
Electronic Transport of Nanographene: Effect of Geometry and Edges
Dr. Katsunori Wakabayashi
【Date & Time】10 June 2009 (Wed) 3:30 pm - 5:00 pm
【Place】8F large seminar room, SENGEN site
【Speaker】Dr. Katsunori Wakabayashi
【Affiliation】NIMS-MANA & JST-PRESTO
【Title】Electronic Transport of Nanographene: Effect of Geometry and Edges
【Abstract】
The successive fabrication of graphene devices has has initiated intensive and diverse research on carbon related systems. The honeycomb crystal structure of single layer graphene consists of two nonequivalent sublattices and results in a unique band structure for the itinerant p-electrons near the Fermi energy which behave as massless Dirac fermion. In graphene, the presence of edges can have strong implications for the spectrum of the p-electrons. In graphene nanoribbons with zigzag edges, localized states appear at the edge with energies close to the Fermi level. In contrast, edge states are absent for ribbons with armchair edges. Recent experiments have succeeded to synthesize graphene nanoribbons using lithography techniques and chemical techniques. In my talk, we focus on edge and geometry effects of the electronic transport properties of graphene nanoribbons. (1) In zigzag nanoribbons, for disorder without inter-valley scattering a single perfectly conducting channel emerges associated with such a chiral mode due to edge states, i.e. the absence of the localization. (2) In armchair nanoribbons, the single-channel transport subjected to long-ranged impurities is nearly perfectly conducting, where the backward scattering matrix elements in the lowest order vanish as a manifestation of internal phase structures of the wavefunction. (3) Nano-graphene junctions are shown to have the zero-conductance anti-resoances associated with the edge states. The relation between the condition of the resonances and geometry is discussed.
【Contact】Dr. Yoshitaka Tateyama
【Place】8F large seminar room, SENGEN site
【Speaker】Dr. Katsunori Wakabayashi
【Affiliation】NIMS-MANA & JST-PRESTO
【Title】Electronic Transport of Nanographene: Effect of Geometry and Edges
【Abstract】
The successive fabrication of graphene devices has has initiated intensive and diverse research on carbon related systems. The honeycomb crystal structure of single layer graphene consists of two nonequivalent sublattices and results in a unique band structure for the itinerant p-electrons near the Fermi energy which behave as massless Dirac fermion. In graphene, the presence of edges can have strong implications for the spectrum of the p-electrons. In graphene nanoribbons with zigzag edges, localized states appear at the edge with energies close to the Fermi level. In contrast, edge states are absent for ribbons with armchair edges. Recent experiments have succeeded to synthesize graphene nanoribbons using lithography techniques and chemical techniques. In my talk, we focus on edge and geometry effects of the electronic transport properties of graphene nanoribbons. (1) In zigzag nanoribbons, for disorder without inter-valley scattering a single perfectly conducting channel emerges associated with such a chiral mode due to edge states, i.e. the absence of the localization. (2) In armchair nanoribbons, the single-channel transport subjected to long-ranged impurities is nearly perfectly conducting, where the backward scattering matrix elements in the lowest order vanish as a manifestation of internal phase structures of the wavefunction. (3) Nano-graphene junctions are shown to have the zero-conductance anti-resoances associated with the edge states. The relation between the condition of the resonances and geometry is discussed.
【Contact】Dr. Yoshitaka Tateyama
Symmetry breaking in superconductors and superfluid : Spin triplet superconductivity in Sr2RuO4
Dr. Youichi Yanase
【Date & Time】20 May 2009 (Wed), 3:30 pm - 5:00 pm
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Youichi Yanase
【Affiliation】Department of Physics, University of Tokyo
【Title】Symmetry breaking in superconductors and superfluid : Spin triplet superconductivity in Sr2RuO4
【Abstract】
Superconductors and superfluid which have multi-component order parameters are the playground of the novel quantum condenced phase leading to the spontaneous symmetry breaking. I will introduce the basic concept of the symmetry breaking in the superconductor/superfluid and talk about the recent developments in this research field. In particular, the spin triplet superconductivity in Sr2RuO4 is discussed in details as a typical example.
【Contact】Dr. Hiroyuki Yamase
【Place】8F large seminar room, Sengen site
【Speaker】Dr. Youichi Yanase
【Affiliation】Department of Physics, University of Tokyo
【Title】Symmetry breaking in superconductors and superfluid : Spin triplet superconductivity in Sr2RuO4
【Abstract】
Superconductors and superfluid which have multi-component order parameters are the playground of the novel quantum condenced phase leading to the spontaneous symmetry breaking. I will introduce the basic concept of the symmetry breaking in the superconductor/superfluid and talk about the recent developments in this research field. In particular, the spin triplet superconductivity in Sr2RuO4 is discussed in details as a typical example.
【Contact】Dr. Hiroyuki Yamase
Finding the global minimum among zillions of local minima : Methods for global geometry optimization of molecular structures
Prof. Stefan Goedecker
【Date & Time】9 April (Thu), 3:30 pm - 5:00 pm
【Place】4F seminar room, Collaborative Res. Bldg., Namiki site
【Speaker】Prof. Stefan Goedecker
【Affiliation】Department of Physics and Astronomy, University of Basel
【Title】Finding the global minimum among zillions of local minima : Methods for global geometry optimization of molecular structures
【Abstract】
The number of local minima grows exponentially with respect to the number of atoms in a molecule or cluster. Finding the global minimum becomes therefore an extremely difficult task for large systems. I will introduce the Minima Hopping method and explain the ingredients which make it efficient. In particular I will discuss the importance of the Bell-Evan-Polyani principle for global optimization. I will also contrast the minima hopping method with two other widely used global optimization methods, namely genetic algorithms and basin hopping.
【Contact】Dr. Yoshitaka Tateyama
【Place】4F seminar room, Collaborative Res. Bldg., Namiki site
【Speaker】Prof. Stefan Goedecker
【Affiliation】Department of Physics and Astronomy, University of Basel
【Title】Finding the global minimum among zillions of local minima : Methods for global geometry optimization of molecular structures
【Abstract】
The number of local minima grows exponentially with respect to the number of atoms in a molecule or cluster. Finding the global minimum becomes therefore an extremely difficult task for large systems. I will introduce the Minima Hopping method and explain the ingredients which make it efficient. In particular I will discuss the importance of the Bell-Evan-Polyani principle for global optimization. I will also contrast the minima hopping method with two other widely used global optimization methods, namely genetic algorithms and basin hopping.
【Contact】Dr. Yoshitaka Tateyama
Free energy calculation for chemical reactions in condensed systems by the QM/MM approach combined with a theory of solutions
Prof. Hideaki Takahashi
【Date & Time】18 March 2009 (Wed), 3:30 pm - 5:00 pm
【Place】8F large seminar room, Sengen site
【Speaker】Prof. Hideaki Takahashi
【Affiliation】Graduate School of Engineering Science, Osaka University
【Title】Free energy calculation for chemical reactions in condensed systems by the QM/MM approach combined with a theory of solutions
【Abstract】
The quantity that governs the reaction pathway in a condensed system is, of course, the free energy change associated with the chemical process. Hence, it is of primary importance to develop an efficient method to compute free energy change for chemical events in many- particle systems. There are, however, two major difficulties in computing the free energy. One is related to the quantum chemical calculations for large systems and another is to the free energy calculation by the method of molecular simulations. Our strategy to overcome these obstacles is to combine the QM/MM approach and a novel theory of solutions termed as the theory of energy representation. Our recent works demonstrated that the approach is efficient and accurate for the computation of the free energies. In this seminar we give the outline of the method and present some applications to chemical reactions in solutions and biological systems.
【Contact】Dr. Tsuyoshi Miyazaki
【Place】8F large seminar room, Sengen site
【Speaker】Prof. Hideaki Takahashi
【Affiliation】Graduate School of Engineering Science, Osaka University
【Title】Free energy calculation for chemical reactions in condensed systems by the QM/MM approach combined with a theory of solutions
【Abstract】
The quantity that governs the reaction pathway in a condensed system is, of course, the free energy change associated with the chemical process. Hence, it is of primary importance to develop an efficient method to compute free energy change for chemical events in many- particle systems. There are, however, two major difficulties in computing the free energy. One is related to the quantum chemical calculations for large systems and another is to the free energy calculation by the method of molecular simulations. Our strategy to overcome these obstacles is to combine the QM/MM approach and a novel theory of solutions termed as the theory of energy representation. Our recent works demonstrated that the approach is efficient and accurate for the computation of the free energies. In this seminar we give the outline of the method and present some applications to chemical reactions in solutions and biological systems.
【Contact】Dr. Tsuyoshi Miyazaki
DFT challenges in catalysis and electrochemistry
Prof. Nicola Marzari
【Date & Time】23 February 2009 (Mon), 3:30 pm - 5:00 pm
【Place】4F seminar room, MANA Bldg., Namiki Site
【Speaker】Prof. Nicola Marzari
【Affiliation】Department of Materials Science and Engineering, Massachusetts Institute of Technology (MIT), USA
【Title】DFT challenges in catalysis and electrochemistry
【Abstract】
Quantum-mechanical simulations based on density-functional theory have become an extremely powerful tool to understand, predict, and design the properties of complex materials or devices. Simulations of many catalytic and electrochemical processes provide nevertheless significant challenges that directly affect our ability to develop new materials for energy storage and conversion from first-principles.
Notwithstanding these successes, there are key qualitative failures that affect the accuracy of calculations based on local or even hybrid exchange-correlation functionals, all rooted in spurious self-interaction errors. I will discuss some of these key challenges, and our suggested solutions, with examples drawn from the study of electron-transfer processes (ferrous-ferric exchange in water) and catalytic reactions at transition-metal complexes (addition-elimination of hydrogen at an iron center).
Last, I will discuss our approach to perform quantum simulations under applied electrochemical potentials (of relevance to fuel-cell reactions) and its application to the study of electrochemical Stark tuning in adsorbates.
【Contact】Dr. Yoshitaka Tateyama
【Place】4F seminar room, MANA Bldg., Namiki Site
【Speaker】Prof. Nicola Marzari
【Affiliation】Department of Materials Science and Engineering, Massachusetts Institute of Technology (MIT), USA
【Title】DFT challenges in catalysis and electrochemistry
【Abstract】
Quantum-mechanical simulations based on density-functional theory have become an extremely powerful tool to understand, predict, and design the properties of complex materials or devices. Simulations of many catalytic and electrochemical processes provide nevertheless significant challenges that directly affect our ability to develop new materials for energy storage and conversion from first-principles.
Notwithstanding these successes, there are key qualitative failures that affect the accuracy of calculations based on local or even hybrid exchange-correlation functionals, all rooted in spurious self-interaction errors. I will discuss some of these key challenges, and our suggested solutions, with examples drawn from the study of electron-transfer processes (ferrous-ferric exchange in water) and catalytic reactions at transition-metal complexes (addition-elimination of hydrogen at an iron center).
Last, I will discuss our approach to perform quantum simulations under applied electrochemical potentials (of relevance to fuel-cell reactions) and its application to the study of electrochemical Stark tuning in adsorbates.
【Contact】Dr. Yoshitaka Tateyama
Re-examination of half-metallic ferromagnetism for doped LaMnO3 in quasiparticle self-consistent GW method
Prof. Takao Kotani
【Date & Time】12 February 2009 (Thur), 10:00 am - 11:30 am
【Place】6F seminar room, Central Bldg., Sengen site
【Speaker】Prof. Takao Kotani
【Affiliation】Department of Applied Mathematics and Physics, Tottori University
【Title】Re-examination of half-metallic ferromagnetism for doped LaMnO3 in quasiparticle self-consistent GW method
【Abstract】
In this talk, we first describe the quasiparticle self-consistent GW (QSGW ) method, which can treat wide range of materials very well. Especially, we applied it to MnO and NiO, and have recently calculated their spin wave dispersions based on the QSGW [1]. They are in good agreement with experiments. Then we now apply it to a cubic virtual-crystal alloy La1-xBaxMnO3 (LBMO) as a theoretical representative for colossal magnetoresistive perovskite manganites. The QSGW predicts LBMO as a fully-polarized half-metallic ferromagnet for a wide range of x and lattice constant. Calculated density of states and dielectric functions are consistent with experiments. In contrast, the energies of calculated spin wave (SW) are very low in comparison with experiments. This is affected neither by rhombohedral deformation nor the intrinsic deficiency in the QSGW method. Thus it will be necessary to include effects due to phonons, which is not included in our calculation, so as to reproduce the experimental SW energies.
[1] T. Kotani and M. van Schilfgaarde,J. Phys.: Condens. Matter 20, 295214 (2008).
[2] T. Kotani and H.Kino,arXiv:0812.4294.
【Contact】Dr. Hiori Kino
【Place】6F seminar room, Central Bldg., Sengen site
【Speaker】Prof. Takao Kotani
【Affiliation】Department of Applied Mathematics and Physics, Tottori University
【Title】Re-examination of half-metallic ferromagnetism for doped LaMnO3 in quasiparticle self-consistent GW method
【Abstract】
In this talk, we first describe the quasiparticle self-consistent GW (QSGW ) method, which can treat wide range of materials very well. Especially, we applied it to MnO and NiO, and have recently calculated their spin wave dispersions based on the QSGW [1]. They are in good agreement with experiments. Then we now apply it to a cubic virtual-crystal alloy La1-xBaxMnO3 (LBMO) as a theoretical representative for colossal magnetoresistive perovskite manganites. The QSGW predicts LBMO as a fully-polarized half-metallic ferromagnet for a wide range of x and lattice constant. Calculated density of states and dielectric functions are consistent with experiments. In contrast, the energies of calculated spin wave (SW) are very low in comparison with experiments. This is affected neither by rhombohedral deformation nor the intrinsic deficiency in the QSGW method. Thus it will be necessary to include effects due to phonons, which is not included in our calculation, so as to reproduce the experimental SW energies.
[1] T. Kotani and M. van Schilfgaarde,J. Phys.: Condens. Matter 20, 295214 (2008).
[2] T. Kotani and H.Kino,arXiv:0812.4294.
【Contact】Dr. Hiori Kino