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Condensed Matter Theory

 Junichi Fukuda, Professor
 Jun Matsui, Lecturer
 Research topic in our group is various phenomena observed in nonequilibrium systems, complex systems and disordered systems. We investigate these phenomena by use of theories based on statistical mechanics and computer simulations. During recent years, we work on unified theory of the glass transition mainly, and we also study a lot of other topics in the statistical physics. Furthermore, we investigate several fundamental problems in the statistical physics through theoretical studies on chemical phenomena.
1. The liquidglass transition of a pure monatomic system  the density functional theory approach 
Glasses are formed by bypassing the crystallization under quenching which is hardly achieved in simple systems such as monocomponent and monatomic (spherical molecule) liquids. At the theoretical point of view, it is important to study these systems as an ideal case. We employ the model molecules which isotropically interact as LennardJones form in short distance and Gaussian in long distance (see in Fig. 1). By tuning the position of Gaussian well into the second neighbor distance of crystal structure, the crystallization can be avoided. The density functional theory of liquids are applied to calculate the solidliquid transition and its coexistent phase.
A. Suematsu et al., J. Chem. Phys., vol. 140 (2014) 244501.
2. The liquidglass transition of a pure monatomic system  moleculardynamics simulation approach 
We test the abovementioned problem by using moleculardynamics simulation. The solidliquid transition points are in good agreements with theoretical calculation. We also find the polyamorphism in phase diagram; low density glass and high density glass are formed by quenching at low and high pressure, respectively.
3. Diffusion and viscosity of solutions
We are interested in approximation theories bridging between statistical physics and hydrodynamics; the boundary conditions, slippy or sticky, how they are determined. We developed to formulate the diffusion and viscosity coefficients of solutions by considering the configuration of solvent molecules around solute, the radial distribution function, g(r), instead of conjecturing the boundary condition on the surface of solute molecules.
Y. Nakamura et al., J. Phys. Soc. Jpn., vol. 83 (2014) 064601.