Interface Computational Science Group

CMS seminar2007

Electronic structure of antiferromagnetic NiO in LDA+DMFT

Dr. Oki Miura
【Date & Time】14 November 2007 (Wed), 3:30 pm - 5:00 pm
【Place】8F larger seminar room, Sengen site
【Speaker】Dr. Oki Miura
【Affiliation】Fujiwara project, JST-CREST
【Title】Electronic structure of antiferromagnetic NiO in LDA+DMFT
【Abstract】
DMFT is based on mapping of many electron systems in bulk onto single impurity problem, where the on-site dynamical interaction is included and the inter-atomic interaction is neglected. The combination of LDA with DMFT, namely LDA+DMFT has been developed and applied to strongly correlated electron systems. In this talk we will show the application of the LDA+DMFT to antiferromagnetic NiO. The on-site Coulomb interaction enhances the hybridization between Ni-3d and O-2p bands and this causes the charge-transfer electronic structure and 4.3eV band gap. These effects obtained by the LDA+DMFT have good agreement with experimental XPS result.
【Contact】Dr. Masao Arai

Recent progress on time-dependent density functional theory within linear response

Dr. Chunping Hu
【Date & Time】24 October 2007 (Wed), 4:00 pm - 5:30 pm
【Place】8F larger seminar room, Sengen site
【Speaker】Dr. Chunping Hu
【Affiliation】Institute for Solid State Physics, The University of Tokyo / JST-CREST
【Title】Recent progress on time-dependent density functional theory within linear response
【Abstract】
Time-dependent density functional theory (TDDFT) has gained enormous popularity in studying electronic excited states. In this seminar our recent research on TDDFT linear response theory will be presented. First we present modified linear response theory to improve TDDFT performance on Rydberg and charge-transfer excitation energies, which are systematically underestimated by conventional TDDFT. Second we present an efficient TDDFT method to calculate nonadiabatic couplings between the ground and excited states, and show that modified linear response theory can be applied to improve the accuracy near potential crossings.
【Contact】Dr. Yoshitaka Tateyama

Physics of Vortex State in Type II Superconductor: From Basics to Applications

Dr. Xiao Hu
【Date & Time】10 October 2007 (Wed), 3:30 pm - 5:00 pm
【Place】8F larger seminar room, Sengen site
【Speaker】Dr. Xiao Hu
【Affiliation】Group Leader of Strong-Coupling Modeling group, NIMS-CMSC
【Title】Physics of Vortex State in Type II Superconductor: From Basics to Applications
【Abstract】
Magnetic field penetrates into type II superconductors as tiny, quantized fluxes associated with supercurrent vortices. Because of the repulsive force, these vortices form a regular pattern, known as the Abrikosov vortex lattice. Dr. Abrikosov got the 2003 Noble Prize for Physics because of this work back to 1957. Physics of vortex states has experienced significant developments since the discovery of high temperature superconductivity in cuprates in 1986. Those who want to know either the basics, or new topics and advanced applications of superconductivity vortex are welcome to the seminar.
【Contact】Dr. Yoshitaka Tateyama

Density functional theory

Prof. Koichi Kusakabe
【Date & Time】2 October 2007 (Tue), 3:30 pm - 5:00 pm
【Place】8F larger seminar room, Sengen site
【Speaker】Prof. Koichi Kusakabe
【Affiliation】Graduate School of Engineering Science, Osaka University
【Title】Density functional theory
【Abstract】
The density functional theory is a theory of the phase transition. The universal density functional given by Levy and Lieb is the first example of a Landau free energy exactly defined at the zero temperature. The single-particle density is the first order parameter in this theory. In this talk, I will show that the multi-reference extension of the Kohn-Sham scheme gives a way to have a self-consistent description of electronic states with multiple order parameters.
【Contact】Dr. Yoshitaka Tateyama

Localized molecular orbital approach to the refractive index and nonlinear optical susceptibility : an ab initio calculation

Dr. Shigeru Suehara
【Date & Time】18 July 2007 (Wed), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Shigeru Suehara
【Affiliation】First-Principles Simulation group (II), NIMS-CMSC
【Title】Localized molecular orbital approach to the refractive index and nonlinear optical susceptibility : an ab initio calculation
【Abstract】
A new hyperpolarizability calculation method based on bond-dipole moment has been developed. Since this method expresses (non)linear response properties in terms of localized molecular orbitals, it offers a chemically intuitive way of explaining these properties. In this seminar, we will introduce this method and present an approach to the origin of nonlinear optical properties of the typical glass forming materials within a classical "electron pair" picture.
【Contact】Dr. Taizo Sasaki

Spinons in spatially anisotropic frustrated antiferromagnets

Dr. Masanori Kohno
【Date & Time】11 July 2007 (Wed), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Masanori Kohno
【Affiliation】Strong-Coupling Modeling group, NIMS-CMSC
【Title】Spinons in spatially anisotropic frustrated antiferromagnets
【Abstract】
Spinons, which are characteristic excitation of one-dimensional systems, have recently been suggested in two-dimensional frustrated antiferromagnets. We explore this possibility through investigation of spatially anisotropic frustrated antiferromagnets using exact results on one-dimensional Heisenberg chains. We find three distinctive spectral features depending on the momentum: (1) one-dimensional spinons which are little influenced by interchain interactions, (2) bound states of spinons, and (3) incoherent excitations. Various unusual features observed in Cs2CuCl4, which can be regarded as an antiferromagnet on a spatially anisotropic triangular lattice, are consistently explained within the framework of the present approach with few adjustable parameters.
M. Kohno, O. A. Starykh, and L. Balents, cond-mat:0706.2012.
【Contact】Dr. Yoshitaka Tateyama

Quantum Monte-Carlo Study of Mn and Mn-oxide clusters

Dr. Hiori Kino
【Date & Time】13 June 2007 (Wed), 3:30 pm - 5:00 pm
【Place】8F larger seminar room, Sengen site
【Speaker】Dr. Hiori Kino
【Affiliation】First-Principles Simulation group (I), NIMS-CMSC
【Title】Quantum Monte-Carlo Study of Mn and Mn-oxide clusters
【Abstract】
Many molecules and clusters of Mn and Mn-oxide have not only interesting physical properties but also can be found in enzymes as important components in biochemical reactions. The electronic structure calculations of these systems are difficult and, for example, choice of exchange-correlation functionals in Density Functional Theory can significantly influence both ground state geometries and spin-state predictions. Therefore, highly accurate calculation is very desirable for these systems. Experimentally, it is established that the Mn dimer is a van der Waals system with weak binding, however, the spin multiplicity has not been settled unambiguously with possibilities covering a range from singlet, triplet, etc, up to 2S+1=11. On the other hand, MnnOn molecules are quite well understood as being a high-spin system, but their geometries depend on the exchange-correlation functionals. We will present our recent results from the fixed-node quantum Monte Carlo calculations of these systems.
【Contact】Dr. Yoshitaka Tateyama

First principles all-electron calculations for excited states of isolated systems using ring and ladder approximation

Dr. Yoshifumi Noguchi
【Date & Time】10 May 2007 (Thur), 3:30 pm - 5:00 pm
【Place】6F seminar room, Sengen site
【Speaker】Dr. Yoshifumi Noguchi
【Affiliation】First-Principles Simulation group (II), NIMS-CMSC
【Title】First principles all-electron calculations for excited states of isolated systems using ring and ladder approximation
【Abstract】
Green’s function method beyond the framework of density functional theory is one of the most efficient methods to accurately treat the excited states of real systems. Particularly, GW approximation (GWA) in which a one-particle self energy operator is approximated as a product of the one-particle Green's function G and the dynamically screened Coulomb interaction W expressed as the ring diagrams up to the infinite order, can accurately estimate a one-electron excited energy. Recently, I applied the spin-polarized GWA to Alkali-metal clusters. In this talk, I will also introduce the ladder approximation (T-matrix) and analyze the Auger spectra of hydrocarbon systems evaluated by T-matrix.
【Contact】Dr. Igor Solovyev

Application of fragment molecular orbital (FMO) method to nano-bio field

Dr. Tatsuya Nakano
【Date & Time】9 March 2007 (Fri), 1:30 pm - 3:00 pm
【Place】8F larger seminar room, Sengen site
【Speaker】Dr. Tatsuya Nakano
【Affiliation】National Institute of Health Sciences / IIS, University of Toky
【Title】Application of fragment molecular orbital (FMO) method to nano-bio field
【Abstract】
Kitaura et al. (Chem. Phys. Lett. 312, 319-324 (1999)) have proposed an ab initio fragment molecular orbital (FMO) method by which large molecules such as proteins can be easily treated with chemical accuracy. In the ab initio FMO method, a molecule or a molecular cluster is divided into M fragments, and the MO calculations on the fragments (monomers) and the fragment pairs (dimers) are performed to obtain the total energy that is expressed as a summation of the fragment energies and inter-fragment interaction energies (IFIEs). In this presentation, I will provide a brief description of the ab initio FMO method and demonstrate recent applications in nano-bio field.
【Contact】Dr. Jun Nara

First principles molecular dynamics simulations of electrochemical reactions

Dr. Minoru Ohtani
【Date & Time】21 February 2007 (Wed), 3:30 pm - 5:00 pm
【Place】8F larger seminar room, Sengen site
【Speaker】Dr. Minoru Ohtani
【Affiliation】Institute for Solid State Physics, University of Toky
【Title】First principles molecular dynamics simulations of electrochemical reactions
【Abstract】
In surface science, because of computational efficiency and tractability, first-principles calculations often use the slab model in which layers of atoms and a vacuum region are periodically repeated. Due to the periodic boundary condition, the slab model is well-known to have the difficulty in handling charged or polarized surfaces. To overcome this, we have developed a new calculation method called effective screening medium (ESM) method. In this seminar I will present details of the ESM method and some recent results for electrochemical reactions.
【Contact】Dr. Yoshitaka Tateyama

Molecular adsorption, foreign atom incorporation, and the formation of superstructures on Si(001)

Prof. Hanchul Kim
【Date & Time】1 February 2007 (Thur), 3:30 pm - 4:30 pm
【Place】6F seminar room, Sengen site
【Speaker】Prof. Hanchul Kim
【Affiliation】Korea Research Institute of Standards and Science
【Title】Molecular adsorption, foreign atom incorporation, and the formation of superstructures on Si(001)
【Abstract】
The Si(001) surface constitutes the most important substrate in the current semiconductor industry, and the decreasing size of the devices demand to develop the atomic-scale controllability. A prerequisite for such an atomic level control is to understand the behavior of the foreign atoms near the surface. In this presentation, I would like to describe a comprehensive understanding on the behavior of carbon atoms, which is achieved by the ab initio pseudopotential total energy calculations and verified by high-resolution scanning tunneling microscopy experiments. The adsorption of small molecules on Si(001) seems to be an apparently easy problem, and has been believed to be fully understood in many cases. Our studies on acetylene (C2H2) and ammonia (NH3) molecules demonstrate that the adsorption structures have only been partly understood. The existence of dimers on Si(001) makes the problem more versatile, and there are multiple adsorption configurations. The adsorbed molecules may be used as a source of foreign atoms upon an appropriate thermal treatment. The dissociated foreign atoms usually modifies the substrate and sometimes produce superstructures on Si(001). In the second half, I would like to focus on the carbon-induced modification of Si(001) and the identification of the atomic structure of the carbon-induced superstructures: 2 xn and c(4 x4). Our study lessons that a careful and accurate investigation is necessary to understand the atomic processes, which is a prerequisite for developing the atomic level controllability.
【Contact】Dr. Taizo Sasaki

Dynamics of driven systems - mode locking, symmetry breaking, and resonance

Prof. Moo Young Choi
【Date & Time】25 January 2007 (Thur), 10:00 am - 11:00 am
【Place】6F seminar room, Sengen site
【Speaker】Prof. Moo Young Choi
【Affiliation】Department of Physics, Seoul National University
【Title】Dynamics of driven systems - mode locking, symmetry breaking, and resonance
【Abstract】
A many-particle system under external drive may display rich dynamic behaviors such as mode locking, dynamic transition, and resonance.
As a physically realizable example, we consider frustrated arrays of superconducting junctions driven by currents. At zero temperature the mode locking phenomena is manifested by giant Shapiro steps in the current-voltage characteristics.
Melting of these steps due to thermal fluctuations is accompanied by a dynamic transition to the disordered state. Also discussed are the characteristic stochastic resonance behavior and vortex motion in response to the driving currents.
【Contact】Dr. Xiao Hu
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