このページではJavaScriptを使用しています。

Research > Material Science

    Computational Material Science
    Graphite sheets (using molecular dynamics simulations) The research and development of useful materials, such as nanoscale materials or semiconductors capable of new functions, is of considerable importance for both science and practical applications. Considering carbon nano-structures, which include carbon nanotubes for example, the included figure shows heat flowing from a high temperature graphite sheet at the bottom of the figure to a low temperature graphite sheet via an atomic bridge. These results are obtained from temperature-controlled molecular dynamics simulations employing precisely expressed potentials governing the forces between the carbon atoms. In this study, the non-equilibrium molecular dynamics methods, which can reduce computational time requirements, are applied to numerical computations of thermal conductivity, which enables us to clarify the thermal conductivity characteristics of various types of nano structures. These nanoscale heat transfer phenomena, which cannot be explained by conventional theories based on the classical macro-scale heat conduction, were discovered by the present research group. Our results offer the possibility of new methods of heat transfer control. This problem is successfully addressed both by physical methods, including non-equilibrium quantum conduction analysis and first-principle electron/thermal conduction simulations, and also by mechanical engineering methods, including thermal conduction and classical molecular dynamics. This problem is thus well suited to the multidisciplinary research approach, which the present research project can afford through its collaboration among various areas of research scientists.

    While the size of semiconductor devices continues to diminish, silicon based devices are approaching their minimum size. Thus, there is an urgent need to replace silicon with an alternative material. Furthermore, for environmental reasons, it has also become important to design devices in non-toxic materials. In order to meet these various requirements, new semiconductor materials are being investigated. For example, one recent result concerns the discovery that a metallic layer is formed at the interface between two particular insulators of differing types. The insulator materials used here are LaAlO3 and SrTiO3, which yield an interesting property that the thicker the insulators, the more metallic the interface becomes. Understanding the mechanism behind this property can be achieved through numerical simulations of electron states. The discovery of other new materials is also expected. If micro properties of the electron states are directly reflected in macro phenomena, holistic computational simulations are an essential research tool for the understanding of the relevant mechanisms and the use of these phenomena in practical applications. However, these numerical simulation techniques have not yet been fully explored, and the number of known methods is limited. It is thus important that, for the development of new practical materials, new numerical simulation methods are introduced and validated.

     Holistic Simulation All matter is composed of a nucleus and electrons, where the nucleus is in turn composed of protons and neutrons. Protons and neutrons are themselves not fundamental, but are composed of quarks and gluons. Thus a nucleon has a structure which changes depending on a nuclear environment. The present project aims to develop the new field provisionally labelled `nucleon molecular dynamics'. This field simulates nuclear states at a basic level by incorporating the degrees of freedom of quarks and gluons inside a nucleon within an antisymmetrized molecular dynamics approach. This new approach considers nuclei from a standpoint that is closer to first principles, and can yield new contributions to nuclear theory. Moreover, by incorporating thermal degrees of freedom, it is possible to apply the method to phase transitions from hadronic matter to quark-gluon plasma in high temperature and/or high density nuclear matter. We also hope to better understand the phenomenon of nuclear fusion in the sun (i.e. a fixed star).

    The cracks in structures and structural materials can ultimately lead to the destruction of the structure. Thus, in order to ensure the safety and reliability of structures, it is of prime importance to understand the dynamical properties of material in the neighbourhood of cracks, and to accurately predict crack propagation. The reader will be aware of events such as the major Hanshin-Awaji earthquake and the more recent accident involving the rupture of pipes at an atomic power station. Concerning the subject of safety in the context of the destruction of structures, one aim of this project is to enhance knowledge of how to ensure the safety of machines and structures, and how to preserve their functionality. This problem has thus far been approached via macro-scale computational simulations using the finite-element method. Analyses and experiments were performed using this method applied to consideration of the dynamical properties of the material at the crack's tip, and empirical laws have been collected to predict specific phenomena. However, these empirical laws cannot be used for predictions of phenomena associated with structures under severe usage, such as high-cycle fatigue breakdowns. There is thus a need to precisely understand the mechanism for crack onset or development, and to use this knowledge to derive a quantitative relationship which can in turn be used for predicting these phenomena.

    The rapid improvement in computers' performance in recent years together with developments in micro-scale numerical simulation methods, as represented by molecular dynamics methods, have made it possible to clarify the fundamental mechanisms governing the behaviour of a material undergoing deformation or destruction. The present project will conduct holistic simulations of crack onset and development from the nano- to micro-scale by large-scale molecular dynamics and transfer dynamics methods. Experimental observations of the micro-scale development and behaviour of cracks will also be undertaken in order to validate the numerical results. The present holistic approach will enable us to predict the crack propagation from a basis in which macro-scale dynamical properties are linked to micro-scale mechanisms. If cracks within a structure can be controlled to a high degree of precision, the safety and reliability of structures can be significantly improved at the design stage.