1,721,008 research outputs found
Speeding up ab initio diffusion Monte Carlo simulations by a smart lattice regularization
Get PDFOne of the most significant drawbacks of the all-electron ab initio diffusion Monte Carlo (DMC) is that its computational cost drastically increases with the atomic number (Z), which typically scales with Z(similar to 6). In this study, we introduce a very efficient implementation of the lattice regularized diffusion Monte Carlo (LRDMC), where the conventional time discretization is replaced by its lattice space counterpart. This scheme enables us to conveniently adopt a small lattice space in the vicinity of nuclei, and a large one in the valence region, by which a considerable speedup is achieved, especially for large atomic number Z. Indeed, the computational performances of the improved LRDMC can be theoretically established based on the Thomas-Fermi model for heavy atoms, implying the optimal Z(similar to 5) scaling for all-electron DMC calculations. This improvement enables us to apply the DMC technique even for superheavy elements (Z >= 104), such as oganesson (Z = 118), which has the highest atomic number of all synthesized elements so far
分布急尖性を考慮した量子モンテカルロ法による原子局所力計算の改善に関する研究
Get PDF物質科学を対象とした量子モンテカルロ法電子状態計算においては、素朴な中心極限定理が成立しない事が明らかとなっている。この事が波動関数の変分最適化や局所力算定における数値的不安定性の原因となる。サンプリングに人為的な重みを導入した拡張アンサンブル法により高次モーメント積分の発散を抑え、エッジワース展開可能な中心極限定理に復元出来る。このような改良化サンプリング法を実装し、変分最適化計算の数値的安定性や収束速度の向上を実証した。 : We implemented an improved sampling method for QMC electronic structure calculations with leptokurtotic behaviour is its sampling distribution. The leptokurtotic property is the origin of the numerical instabilities in variational opitimizations and evaluations of local forces. Some appropriate extended ensamble sampling is proved to give better numerical stability and faster convergence in the variational optimization.研究種目：若手研究（Ｂ）研究期間：2010～2011課題番号：22760061研究者番号：40354146研究分野：物性理論科研費の分科・細目：応用物理学・工学基礎/工学基
固体系拡散モンテカルロ法の開発
Get PDF以下につき成果を論文に出版した：固体周期系量子モンテカルロ計算によるダイアモンド固体の基礎物性計算、固体標準模型上のハバードのＵパラメタの成因、ポルフィリン遷移金属錯体の擬ポテンシャル高精度計算、フラグメント法とQMC法を組合わせた方法論の開発。スピン偏極下での多体摂動法による励起スペクトル。以下は進行中の題目である：一様媒質に埋込まれた原子の計算、珪素固体の基礎物性計算。AlN, GaN, InNなど窒化物のバンドギャップ評価。研究種目：特定領域研究研究期間：2005～2008課題番号：17064016研究者番号：40354146研究分野：物理学科研費の分科・細目：物理学・数理物理・物性基
ノード内並列に適した量子モンテカルロ電子状態計算の新しい配位更新法の開発と検証
Get PDF当該モンテカルロ法で用いられる配位更新においては、全ての粒子位置を斉次に更新する事は必ずしも必要ではないため、一つ一つを逐次的に更新する方法が一般的に広く採用されている。この逐次更新では、着目粒子以外の粒子位置について現段/前段の位置のいずれを採用するかに自由度があり、前段位置を採用することで新たな並列多重度を生み出せる。本研究では、この並列多重度にGPUのメニーコア並列化を適用する事で、当該サブルーチン部分に数十倍に高速化を実現する事に成功した。 : We considered a new updating scheme for particle positions appearing in Monte Carlo methods, which is suitable for the GPGPU acceleration. In the particle-by-particle Metropolis updating scheme, we can evaluate whether a proposed update of a particle position was accepted or rejected base on the configuration of other particles at the previous step, though most of the conventional implementation uses those at the present step. By taking the previous step configuration, we can create the considerable number of degrees for further internal parallel processing. We implemented the internal parallel processing using GPGPU further on the conventional MPI implementation, and achieved the reasonable acceleration.研究種目：挑戦的萌芽研究研究期間：2013～2014課題番号：25600156研究者番号：40354146研究分野：物性理論, 計算物理
3次元電子正孔系におけるポリ励起子相出現可能性の理論的解明
Get PDF拡散モンテカルロ法を用い電子正孔ガスの相図を解明した。「実効相互作用＋励起子複合体のみの波動関数」と記述し、「電子正孔質量比(量子ダイナミクス効果)」と「実効相互作用の遮蔽パラメタ(電子相関効果)」の2パラメタ空間で相図を構成し「ドナー不純物に束縛される励起子の安定化程度」に基本的な情報を提供した。電子ガス模型での展開と並行し、層状カルコゲナイドなど遷移金属化合物系層状物質の解析にも研究展開し、具体的なバンド構造から有効質量模型に持ち込む過程で非自明な不安定格子振動モードを発見するなどの成果を得た。：Phase diagrams of electron-hole systems are investigated by using diffusion Monte Carlo method. The system is modelled by the effective inter-particle interactions with tunable parameters for the Coulombic screenings and the mass ratio between electrons and holes. A phase diagram is evaluated as a function of the screening strength (representing electronic correlation effect) and the mass ratio (quantum dynamics of nuclei). It may describe how much stable when an exciton is bound by a donor impurity in semiconductors. As well as the work on electron-hole models, we worked on real materials, such as layered pnictides, to estimate realistic parameters for the ratio and screening effects. On the investigations, we found the lattice instability through its phonon properties and made an successful explanation of the experimental facts under intensive debates about the origin of the instability.基盤研究(B)（一般）研究期間：2014～2016課題番号：26287063研究者番号：40354146研究分野：多体電子論、量子エレクトロニク
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Optimization of Many-Body Wave Function
Get PDFAn overview on recent technical aspects of ab-initio electronic structure calculations using Quantum Monte Carlo is given in this article. In order to treat realistic, inhomogeneous, and larger systems within the practical calculational cost, several important techniques have been developed for the method. The article explains variety of many-body wavefunction form and the optimization schemes applied to the recent works mainly on extended periodic systems. Selected data are given to show how the optimization works to improve ground state energy
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