第119回計算科学コロキウムを、11月27日（月）に開催いたします。
多数のご来聴をお願いいたします。

場所：筑波大学　計算科学研究センター　ワークショップ室
日時：2017年11月27日（月）10:00-11:30
講演タイトル：Finding Regularity in Problems with Irregularity
講演者氏名：中島浩（京都大学・学術情報メディアセンター・教授）
使用言語：日本語

要旨：Vectorized computation especially on scalar processors with wide SIMD mechanism requires regularity. For example, though such a processor has gather/scatter capability for irregular memory accesses, they are much less efficient than ordinary consecutive accesses mainly due to, in speaker’s opinion, the line-oriented configuration of caches. Unfortunately, real HPC programs often have such irregular accesses to a vector multiplied to a sparse matrix in CRS format, to a linear list to represent a set of objects, and so on, and thus fail to exploit SIMD-vector mechanism efficiently. However, HPC problems (not programs) with sparse matrices, dynamically configured sets, etc. may have some degree of regularity because such objects can be represented in some form with regularity. In this talk, a few examples in which regularity is found and exploited are presented to discuss the importance of programming effort and of the way to reduce the amount of efforts made by programmers.

世話人：朴 泰祐　

第118回計算科学コロキウムを、10月25日（水）に開催します。
多数のご来聴をお願い致します。

場所：筑波大学　計算科学研究センター　会議室D
日時：2017年10月25日 （水）16:00-18:00
講演タイトル：Theoretical Vibrational Spectroscopy of Aqueous TMAO Solution under High Hydrostatic Pressure Conditions
講演者氏名：井本翔博士(ルール大学ボーフム)
使用言語：英語

 

要旨：Hydrogen bonds (H-bonds) play a significant role in liquid water, aqueous solutions, and bio-systems and, therefore, a deep understanding of H-bonds in liquid phases is of great importance. Although many theoretical and experimental studies have been devoted to understand their properties at ambient conditions, our knowledge of H-bonds under extreme conditions, such as high hydrostatic pressure (HHP) conditions in the kilo-bar regime, is not enough. Especially, the pressure response of aqueous trimethylamine N-oxide (TMAO) is of great interest because it works as a protecting osmolyte against high pressure denaturation. Vibrational spectroscopy is one of the most powerful methods to elucidate structure and dynamics of H-bonds. Concerning the theoretical side, quantitative analysis on IR spectra of H-bonding systems requires not only atomistic trajectories but also accurate dipole moments because the effects of induced dipole moments and charge transfer are not negligible in these cases. In this study, by using ab initio MD simulations, we analyzed IR spectra of TMAO(aq) under HHP conditions. The solvation structure of TMAO-oxygen changes dramatically under HHP conditions; threefold H-bonding structure is dominant at 1 bar, whereas three and fourfold H-bonding structures are almost equally populated at 10 kbar [1,2]. We found that the increase in the number of H-bonds can be observed as a skewness of the N-O stretch spectra since three and fourfold H-bonding structures have slightly different resonance frequencies [3]. 

[1] S. Imoto, H. Forbert, D. Marx, Phys. Chem. Chem. Phys. 17, 24224 (17). 
[2] C. Hölzl, P. Kibies, S. Imoto, R. Frach, S. Suladze, R. Winter, D. Marx, D. Horinek, S. M. Kast, J. Chem. Phys. 144, 144104 (2016).
[3] S. Imoto, P. Kibies, C. Rosin, R. Winter, S. M. Kast, D. Marx, Angew. Chem. Int. Ed. 55, 9534 (2016).

 

世話人：重田育照　

懇親会：　18:30からつくばセンター界隈で懇親会を行います。

参加希望なされる方は10/23までに庄司 (mshoji[at]ccs.tsukuba.ac.jp)まで、

ご連絡頂けますようお願い致します。

第117回計算科学コロキウムを、10月13日（金）に開催します。
多数のご来聴をお願い致します。

場所：筑波大学　総合研究棟B 110
日時：2017/10/13(金)　16:00-17：00
講演タイトル：Molecular Modeling of Water-Air and Ice-Air Interfaces
講演者氏名：永田勇樹　博士
講演者所属：Max Planck Institute for Polymer Research, Bonn Group

要旨：Structure and dynamics of Interfacial water  governs the atmospheric chemistry, chemical reactions on aqueous interface, and high surface tension of water. Nevertheless, molecular level insight into interfacial water is not fully gained. In this talk, I shall focus on the two topics – water evaporation and anomaly of ice surface around 200 K -. For water evaporation, I would reveal that water evaporation is -NOT- a completely stochastic process. The evaporation of water occurs in a time-ordered motion of multiple water molecules. [1] This challenges the variability of the free energy description for such an event. For anomaly of ice surface, we combined the molecular dynamics simulation with sum-frequency generation spectroscopy [2] and reveal that ice surface generates the maximum number of the hydrogen bond around 200 K, [3] which seems counterintuitive for the entropy increase in the thermodynamics second law. I will discuss how ice surface is melt with increasing temperature.

[1] Y. Nagata, K. Usui, and M. Bonn, Phys. Rev. Lett. 115, 236102 (2015)
[2] F. Perakis, …, Y. Nagata, Chem. Rev. 116, 7590 (2016)
[3] W. J. Smits, T. Fujie, …, Y. Nagata, Phys. Rev. Lett. 119, 133003 (2017)