第107回計算科学コロキウムを、5月18日（水）に開催します。
多数のご来聴をお願い致します。
なお、今回はCS専攻との共催となっており、開催場所が異なりますのでご注意ください。

日時：2016年5月18日（水）15:00-16:00
場所：総合研究棟B棟1001　（SB1001）
題目：Big Data Research Opportunities in Disaster Management:
The LITMUS Landslide Information Service as an Illustrative Example
講師：Prof. Calton Pu
Georgia Institute of Technology (Professor and J.P. Imlay, Jr. Chair in Software)

要旨:
The ongoing convergence of evolution of devices (Internet of Things), deployment of large shared infrastructures (computing clouds), and accumulation of Big Data (sensors and social media) has created exciting new research challenges in quality of service (e.g., real-time response time, high availability and robustness despite widespread failures), and quality of information (e.g., security, privacy, and robustness despite misinformation). These research challenges require integration and synthesis of results from several related areas, e.g., sensor networks and social networks as Big Data producers, sophisticated machine learning models running on clouds as Big Data consumers, and system support at various levels to provide timely response. We have built LITMUS, a landslide detection system, to illustrate the research challenges of integrating physical sensors (earthquakes and rainfall) and social sensors (Twitter, Instagram, and YouTube). LITMUS is running live in the project website at [<grait-dm.org>].

世話人：北川博之

共催：CS専攻

第106回計算科学コロキウムを、4月15日（金）に開催します。
多数のご来聴をお願い致します。

日時：2016年4月15日（金）13:30-15:00
場所：筑波大学計算科学研究センター 会議室A
題目：Strong light-matter interaction in materials science: merging QED and TDDFT
講師：Prof. Dr. Angel Rubio
Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany
NanoBio Spectroscopy Group and ETSF Scientific Development Centre, Universidad del País Vasco, UPV/EHU San Sebastián, Spain
FHI Max-Planck-Gesellschaft, Berlin, Germany

要旨:
Computer simulations that predict the light-induced change in the physical and chemical properties of complex systems, molecules, nanostructures and solids usually ignore the quantum nature of light.
We have recently shown how the effects of the photons can be properly included in such calculations. The basic idea is to treat the full QED system of particles and photons as a quantum fluid. Here the particles are represented by a charge current, and the photons by a classical electromagnetic field that acts on the current in a very complex manner. This study opens up the possibility to predict and control the change of material properties due to the interaction with light particles from first principles.

Here we will review the recent advances within density-functional a schemes to describe spectroscopic properties of complex systems with special emphasis to modeling time and spatially resolved electron spectroscopies. We will discuss the theoretical approaches developed in the group for the characterization of matter out of equilibrium, the control material processes at the electronic level and tailor material properties, and master energy and information on the nanoscale to propose new devices with capabilities. We will focus on examples linked to the efficient conversion of light into electricity or chemical fuels (“artificial photosynthesis”) and the design on new nanostructure based optoelectronic devices, among others.

Our goal is to provide a detailed, efficient, and at the same time accurate microscopic approach for the ab-initio description and control of the dynamics of decoherence and dissipation in quantum many-body systems. This theoretical framework provides a new way to control and alter chemical reactions in complex systems, direct the movement of electrons, selectively trigger physico-chemical processes, and create new state of matter.

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Kohn-Sham Approach to Quantum Electrodynamical Density Functional Theory: Exact Time-Dependent Effective Potentials in Real Space J. Flick, M. Ruggenthaler, H. Appel, A. Rubio, Proceedings of The National Academy of Sciences of The United States of America 112 15285-15290 (2015)

Optimized Effective Potential for Quantum Electrodynamics Time-Dependent Density Functional Theory C. Pellegrini, J. Flick, I. V. Tokatly, H. Appel and A. Rubio, Physical Review Letters 115, 093001 (2015)

Quantum Electrodynamics Density-Functional Theory: Bridging Quantum Optics and Electronic-Structure Theory M. Ruggenthaler, J. Flick, C. Pellegrini, H. Appel, I. V. Tokatly, A. Rubio, Physical Review A 90 012508-1,26 (2014)

Coherent ultrafast charge transfer in an organic photovoltaic blend S. Maria Falke, C.A. Rozzi, D. Brida, M. Amato, A. De Sio, A. Rubio, G. Cerullo, E. Molinari, C. Lienau, Science 344 1001-1005 (2014)

Insights into the modulation of light absorption by chlorophyll in green plant, Physical Chemistry Chemical Physics 17, 26599 – 26606 (2015) and Unraveling the Intrinsic Color of Chlorophyll, Angewandte Chemie International Edition 54, 2170-2173 (2015)

世話人：矢花一浩

第105回計算科学コロキウムを、4月4日（月）に開催します。
多数のご来聴をお願い致します。

日時：2016年4月4日（月）15:00-16:30
場所：筑波大学計算科学研究センター 会議室A
題目：Highly Frustrated Spin-Lattice Models of Magnetism and Their Quantum Phase Transitions: A Microscopic Treatment via the Coupled Cluster Method
講師：Dr. Raymond F. Bishop (School of Physics and Astronomy, The University of Manchester)

要旨:
The coupled cluster method¹⁾ (CCM) is one of the most pervasive, most powerful, and most successful of all ab initio formulations of quantum many-body theory. It has probably been applied to more systems in quantum field theory, quantum chemistry, nuclear, subnuclear, condensed matter and other areas of physics than any other competing method. The CCM has yielded numerical results which are among the most accurate available for an incredibly wide range of both finite and extended physical systems defined on a spatial continuum. These range from atoms and molecules of interest in quantum chemistry, where the method has long been the recognized “gold standard”, to atomic nuclei; from the electron gas to dense nuclear and baryonic matter; and from models in quantum optics, quantum electronics, and solid-state optoelectronics to field theories of strongly interacting nucleons and pions.

This widespread success for both finite and extended physical systems defined on a spatial continuum²⁾ has led to recent applications to corresponding quantum-mechanical systems defined on an extended regular spatial lattice. Such lattice systems are nowadays the subject of intense theoretical study. They include many examples of systems characterised by novel ground states which display quantum order in some region of the Hamiltonian parameter space, delimited by critical values which mark the corresponding quantum phase transitions. The quantum critical phenomena often differ profoundly from their classical counterparts, and the subtle correlations present usually cannot easily be treated by standard many-body techniques (e.g., perturbation theory or mean-field approximations). A key challenge for modern quantum many-body theory has been to develop microscopic techniques capable of handling both these novel and more traditional systems. Our recent work shows that the CCM is capable of bridging this divide. We have shown how the systematic inclusion of multispin correlations for a wide variety of quantum spin-lattice problems can be efficiently implemented with the CCM.³⁾ The method is not restricted to bipartite lattices or to non-frustrated systems, and can thus deal with problems where most alternative techniques, e.g., exact diagonalisation of small lattices or quantum Monte Carlo (QMC) simulations, are faced with specific difficulties.

In this talk I describe our recent work that has applied the CCM to strongly interacting and highly frustrated spin-lattice models of interest in quantum magnetism, especially in two spatial dimensions. I show how the CCM may readily be implemented to high orders in systematically improvable hierarchies of approximations, e.g., in a localised lattice-animal-based subsystem (LSUBm) scheme, by the use of computer-algebraic techniques. Values for ground-state (and excited-state) properties are obtained which are fully competitive with those from other state-of-the-art methods, including the much more computationally intensive QMC techniques in the relatively rare (unfrustrated) cases where the latter can be readily applied. I describe the method itself, and illustrate its ability to give accurate descriptions of the ground-state phase diagrams of a wide variety of frustrated magnetic systems via a number of opical examples of its high-order implementations, from among a very large corpus of results for spin lattices. The raw LSUBm results are themselves generally excellent. I show explicitly both how they converge rapidly and can also be accurately extrapolated in the truncation index, m → ∞, to the exact limit.
_____________________________________________________________
1) R.F. Bishop, in Microscopic Quantum Many-Body Theories and Their Applications, (eds. J. Navarro and A. Polls), Lecture Notes in Physics Vol. 510, Springer-Verlag, Berlin (1998), 1.
2) R.F. Bishop, Theor. Chim. Acta 80 (1991), 95; R.J. Bartlett, J. Phys. Chem. 93 (1989), 1697.
3) D.J.J. Farnell and R.F. Bishop, in Quantum Magnetism, (eds. U. Schollwöck, J. Richter, D.J.J. Farnell and R.F. Bishop), Lecture Notes in Physics Vol. 645, Springer-Verlag, Berlin (2004), 307.

世話人：中務 孝