第105回計算科学コロキウムを、4月4日（月）に開催します。
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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.
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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

第104回計算科学コロキウムを、12月11日（金）に開催します。
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日時：2015年12月11日（金）16:00-17:30
場所：筑波大学計算科学研究センター 会議室A
題目：The Interaction of HPC Programming Models with Interconnect Capabilities
講師：Dr. Khaled Ibrahim (Lawrence Berkeley National Laboratory)

要旨:
HPC systems are growing in heterogeneity due to power consumption constraints. Such trend makes the use of hybrid-programming models a requirement to achieve efficiency. Moreover, inter-node and intra-node communication are traditionally thought of as orthogonal problems, leading to suboptimal performance.

In this talk, we present internal design changes we made to GASNet communication library to have better interoperability of intra-node shared memory programming models, such as OpenMP, with partition global address space (PGAS) programming models. We also discuss the interaction of PGAS models and MPI two-sided with interconnects that leverage relaxed ordering of transfers to improve performance. We show how programming model semantics influence the possible runtime optimization strategy on such interconnects.

We also discuss how programming models (tasking vs. bulk synchronous) could influence the volume of data movement at scale.

Finally, we shed some light on ongoing GASNet-EX specification activities that aim to radically enhance the functionalities and interfaces of GASNet.

世話人：朴 泰祐

第103回計算科学コロキウムを、12月10日（木）に開催します。
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日時：2015年12月10日（木）9:30-12:00
場所：筑波大学計算科学研究センター 会議室B
題目：アミノ酸の安定構造と分子解離に繋がる多段階異性化反応経路の効率的自動探索法の開拓
講師：岸本　直樹 氏（東北大学大学院理学研究科化学専攻・准教授）

要旨:
内部エネルギーを持つ分子の解離反応経路は、化学研究者の経験ではカバーできないほど多くの異性化反応経路に分岐して複数の解離生成物へ繋がっており、解離反応経路の研究を困難にしてきた。また、異性化を経た後の解離反応では、生成物の構造を実験で特定することは困難である。
　私は本研究 で、分子の安定構造とその解離反応経路の量子化学計算方法を確立することで、ユーザーが試行錯誤を極力しない自動化を目指している。

世話人：重田育照

第102回計算科学コロキウムを、10月21日（水）に開催します。
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日時：2015年10月21日 (水）10:00-11:30
場所：筑波大学計算科学研究センター 会議室B
題目：Multi-modal Dynamic Cross Correlation法の開発と転写因子–DNA複合体における動的相関ネットワークの解析
講師：笠原 浩太 氏（大阪大学）

要旨:
分子動力学法は分子系の微視的な動的特性を理解するための有効な手段の一つである。
しかしながらその結果得られるデータの解釈は容易でなく、単純なアンサンブル平均による議論では過渡的な運動モードの変化など多峰性の分布を生ずる重要な現象を見落としてしまう。本研究では従来のDynamic Cross Correlation (DCC) 法を拡張したMulti-modal DCC (mDCC)法を開発し、このような多峰性分布の自動検出を可能とした。
これを転写因子–DNA複合体に応用し、分子内相互作用ネットワークの解析を行ったのでこれを発表する。

世話人：重田育照

第101回計算科学コロキウムを、6月9日（火）に開催します。
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日時：2015年6月9日（火）14:00-16:00
場所：筑波大学計算科学研究センター 会議室A
題目：MPI Communication Challenges in Irregular Data-Driven Applications
講師：Dr. Pavan Balaji, Argonne National Laboratory, USA

概要：Modern applications are increasingly moving towards an irregular data-driven computational model where how they compute and which processes they communicate with fundamentally relies on the data being processed. This results in frequent communication of small data elements with a large number of processes, ability to process such messages asynchronously and on-demand, notions of latency-hiding by leveraging very deep queues of outstanding operations and the capability to perform efficient communication when hundreds of threads try to communicate simultaneously. In this talk, I’ll first discuss some of the large computational applications at Argonne and their computational trends. Then I’ll discuss some of the optimizations that we are exploring within the MPI library to address these challenges, while looking forward to where these applications are planning to evolve to in the next few years.

世話人：朴 泰祐