研究者詳細 - 松本　正和

Order parameters for the multistep crystallization of clathrate hydrates 査読

Liam C. Jacobson, Masakazu Matsumoto, Valeria Molinero

Journal of Chemical Physics 135 ( 7 ) 2011年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

Recent reports indicate that the crystallization of clathrate hydrates occurs in multiple steps that involve amorphous intermediates and metastable clathrate crystals. The elucidation of the reaction coordinate for clathrate crystallization requires the use of order parameters able to identify the reactants, products, and intermediates in the crystallization pathway. Nevertheless, existing order parameters cannot distinguish between amorphous and crystalline clathrates or between different clathrate crystals. In this work, we present the first set of order parameters that discern between the sI and sII clathrate crystals, the amorphous clathrates, the blob of solvent-separated guests and the liquid solution. These order parameters can be used to monitor the advance of the crystallization and for the efficient implementation of methods to sample the rare clathrate nucleation events in molecular simulations. We illustrate the use of these order parameters in the analysis of the growth and the dissolution of clathrate crystals and the spontaneous nucleation and growth of clathrates under conditions of high supercooling. © 2011 American Institute of Physics.

DOI： 10.1063/1.3613667

On the Structure Selectivity of Clathrate Hydrates 査読

Masakazu Matsumoto, Hideki Tanaka

JOURNAL OF PHYSICAL CHEMISTRY B 115 ( 25 ) 8257 - 8265 2011年6月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

We propose a strategic method to search for a new clathrate hydrate by investigating the selectivity of its crystalline structure, which has been expected to depend mostly on the guest species and less on the thermodynamic conditions. Relative stability among various morphologies is examined in terms of the chemical potential of water of clathrate hydrates in equilibrium with guest gases. This evaluation is performed by calculating the free energy of cage occupancy according to the standard statistical mechanical theory with the aid of the Yarmolyuk and Kripyakevich's rule on the Frank-Kasper type alloys to estimate the numbers of cages of various types. Thus, a comprehensive interpretation of the selectivity of crystalline structures is successfully made. We explain why two major structures are stable in most of the thermodynamic conditions and establish a relation between polymorphism of clathrate hydrate and the guest size and other parameters, thereby suggesting a way to find a new clathrate hydrate by appropriate choice of the guest species and/or the thermodynamic properties. It is found that there is a small room in the above parameter space for the other structure than the major two to be the most stable, including a new structure. In addition, simple but thorough elucidation is given for preferential formation of TS-I structure in bromine hydrate.

DOI： 10.1021/jp203478z

Four-body cooperativity in hydrophonic association of methane 査読

Matsumoto, M.

Journal of Physical Chemistry Letters 1 ( 10 ) 1552 - 1556 2010年5月

Why does water expand when it cools? 査読

Matsumoto, M.

Physical Review Letters 103 ( 1 ) 2009年7月

Network motif of water

Masakazu Matsumoto, Akinori Baba, Iwao Ohmine

COMPLEX SYSTEMS-BOOK 1 982 219 - + 2008年

担当区分：筆頭著者,　最終著者,　責任著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：AMER INST PHYSICS

The network motif of water, vitrite, is introduced to elucidate the intermediate-range order in supercooled liquid water. Unstrained vitrites aggregate in supercooled liquid water to form very stable domain. Hydrogen bond rearrangements mostly occur outside the domain, so that the dynamical heterogeneity also stands out. Pre-peak in the structure factor of low density amorphous ice is reproduced by inter-vitrite structure factor. The vitrite can therefore be regarded as a plausible building block of the intermediate-range order and heterogeneity in supercooled liquid water and low-density amorphous ice.

Topological building blocks of hydrogen bond network in water 査読

M. Matsumoto, A. Baba, I. Ohmine

JOURNAL OF CHEMICAL PHYSICS 127 ( 13 ) 134504 2007年10月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

Basic three-dimensional units of the network, called fragments, are introduced to characterize the hydrogen bond (HB) network structure of water. Topological differences among normal liquid water, water at low temperature, and water under high pressure are elucidated by their fragment statistics. Water at low temperature has almost defect-free network and is filled with stable fragments with small distortion. It is found that there exists a certain way on how fragments mutually aggregate. Well-formed aggregates heterogeneously constitute very stable network structures. HB network rearrangements occur scarcely inside these aggregated domains but take place in their surface areas. The heterogeneity of HB structure and rearrangement in water is thus explained in terms of the fragment structure and its rearrangements. The fragment analysis thus elucidates the intermediate-range order in water HB network. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2772627

Relevance of hydrogen bond definitions in liquid water 査読

Masakazu Matsumoto

JOURNAL OF CHEMICAL PHYSICS 126 ( 5 ) 054503-1 - 054503-6 2007年2月

担当区分：筆頭著者,　最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

To evaluate the relevance of treating the hydrogen bonds in liquid water as a digital (discrete) network and applying topological analyses, a framework to optimize the fitting parameters in various hydrogen bond definitions of liquid water is proposed. Performance of the definitions is quantitatively evaluated according to the reproducibility of hydrogen bonding in the inherent structure. Parameters of five popular hydrogen bond definitions are optimized, for example. The optimal choice of parameters for the hydrogen bond definitions accentuates the binary nature of the hydrogen bonding and the intrinsic network topology of liquid water, especially at the low temperature region. The framework provides a solid basis for network analyses, which have been utilized for water, and is also useful for designing new hydrogen bond definitions. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2431168

Molecular dynamics simulation of the ice nucleation and growth process leading to water freezing 査読

Masakazu Matsumoto, Shinji Saito, Iwao Ohmine

Nature 416 ( 6879 ) 409 - 413 2002年3月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Upon cooling, water freezes to ice. This familiar phase transition occurs widely in nature, yet unlike the freezing of simple liquids, it has never been successfully simulated on a computer. The difficulty lies with the fact that hydrogen bonding between individual water molecules yields a disordered threedimensional hydrogen-bond network whose rugged and complex global potential energy surface permits a large number of possible network configurations. As a result, it is very challenging to reproduce the freezing of 'real' water into a solid with a unique crystalline structure. For systems with a limited number of possible disordered hydrogen-bond network structures, such as confined water, it is relatively easy to locate a pathway from a liquid state to a crystalline structure. For pure and spatially unconfined water, however, molecular dynamics simulations of freezing are severely hampered by the large number of possible network configurations that exist. Here we present a molecular dynamics trajectory that captures the molecular processes involved in the freezing of pure water. We find that ice nucleation occurs once a sufficient number of relatively long-lived hydrogen bonds develop spontaneously at the same location to form a fairly compact initial nucleus. The initial nucleus then slowly changes shape and size until it reaches a stage that allows rapid expansion, resulting in crystallization of the entire system.

DOI： 10.1038/416409a

Landscape of water dynamics and chemical reactions 査読

Ohmine I, Matsumoto M, Saito S, Baba A, Yonekura Y, Ogasawara S, Inagaki H, Kobayashi C

NEW KINDS OF PHASE TRANSITIONS: TRANSFORMATIONS IN DISORDERED SUBSTANCES 81 613 - 622 2002年

Global potential energy surfaces of water clusters; Reaction coordinate and annealing analyses

A Baba, J Tanaka, S Saito, M Matsumoto, Ohmine, I

JOURNAL OF MOLECULAR LIQUIDS 77 ( 1-3 ) 95 - 103 1998年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

A global nature of the potential energy surface (PES) of water clusters, (H2O)(20) and (H2O)(54) was investigated by using a reaction coordinate analysis and an annealing method. It was shown for (H2O)(64) that the successive reaction coordinates passing through low energy barriers lead to a deep minimum and the overall potential has so called a funnel structure, similar to PES of a protein folding. On the other hand, the smaller cluster (H2O)(20) has the rugged PES of a 'fragile' type, resulting from distinct bond reordering. (C) 1998 Elsevier Science B.V.

DOI： 10.1016/S0167-7322(98)00070-1

A new approach to the dynamics of hydrogen bond network in liquid water 査読

M Matsumoto, Ohmine, I

JOURNAL OF CHEMICAL PHYSICS 104 ( 7 ) 2705 - 2712 1996年2月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

The relation between topology and rearrangement dynamics of the hydrogen bond network (HEN) in the supercooled liquid water is investigated by using molecular dynamics (MD) calculation and examining topological indices. We have found that there is very strong correlation among certain pairs of hydrogen bonds.; HBN is shown to be represented by an ''undirected'' graph. Topology and rearrangement dynamics of HBN are then simply described in terms of the network defects and their motions. Based on this fact, a new lattice dynamic model is proposed. The model shows that spontaneous heterogeneous hydrogen bond rearrangement occurs even when the network structure is homogeneous. (C) 1996 American Institute of Physics.

DOI： 10.1063/1.471664

Acetonitrile pair formation in aqueous solution 査読

Masakazu Matsumoto, Hideki Tanaka, Koichiro Nakanishi

The Journal of Chemical Physics 99 ( 9 ) 6935 - 6940 1993年11月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AIP Publishing

Extended reference interaction site model (RISM) theoretical calculations and molecular dynamics simulation have been carried out for dilute aqueous solution of acetonitrile. Potential of mean force between two solute molecules was calculated. Two solute molecules tend to associate with each other by an attractive interaction between two negatively charged nitrogen atoms. It is found that ''bifurcated hydrogen bonds'' between a hydrogen atom on a water molecule and nitrogen atoms on acetonitrile molecules play an important role in the solute-solute interaction.

DOI： 10.1063/1.465838