Keiichi Takase

Liquid Structure of 1-Propanol by Molecular Dynamics Simulations and X-Ray Scattering

Molecular dynamics (MD) simulations and X-ray scattering experiments have been carried out on liquid 1-propanol. The radial distribution functions obtained from these two methods were in good agreement with each other. On the basis of the hydrogen-bond number and the angular correlation functions of the four sequentially hydrogen-bonded O atoms derived from the MD calculation, it was found that the hydrogen-bonded O atoms preferentially form a planar zigzag chain structure, but that the plane undulates like a wave.

Thermal conductivity of molten alkali halides: Temperature and density dependence

The thermal conductivities of a series of molten alkali halides have been evaluated by using molecular dynamics simulation within the framework of Fumi-Tosi potential models. Although the calculated results showed 0%-50% larger values than experimental results depending on system, they are in agreement with each other in showing both negative temperature and ionic mass dependence. In order to clarify the cause of the negative temperature dependence in more detail, the thermal conductivity under constant temperature or constant density was evaluated for all alkali chlorides and all sodium halides. The calculations reveal that the thermal conductivity depends strongly on density but only weakly on temperature. While the integrated value of the autocorrelation function for energy current increases with temperature, this is canceled out by the reciprocal temperature factor in relation to the thermal conductivity. With increasing density the integrated value increases, and this dominates the behavior of the thermal conductivity. By repeating the calculations with different ionic masses, we have concluded that the thermal conductivity is a function of m(-1/2)(N/V)(2/3), where m is the geometric mean of ionic mass between anion and cation and N/V is the number density.

Short-range structure of alkaline-earth borate glasses by pulsed neutron diffraction and molecular dynamics simulation

Abstract The structure of vitreous MO· n B 2 O 3 (M=Ca and Ba; n =2, 3 and 4) has been studied by pulsed neutron diffraction measurement with the help of molecular dynamics (MD) simulation. The first and second peaks assigned to the nearest-neighbor B–O and O–O correlations, respectively, in the obtained total pair distribution functions shifted little with increasing MO content, while the asymmetry of the first peak increased significantly with MO content; these results are different from those for potassium borate glasses. It was inferred that the BO 3 and BO 4 units are better defined in these alkaline-earth borate glasses than those in the potassium borate glasses. Both the full-width at half maximum (FWHM) of the first peak and the average co-ordination number of O around B clearly increased as MO content increased which is the same behavior with alkali borate glasses. The fraction of four-co-ordinated B showed a larger deviation from x /(1− x ) for CaO–B 2 O 3 glasses than that for BaO–B 2 O 3 glasses which shows a different dependence of the deviation on cation size from that in alkali borate glasses, and is in good agreement with the results from MD simulation.

Thermal conductivity in molten alkali halides: composition dependence in mixtures of (Na–K)Cl

The thermal conductivities of molten (Na–K)Cl systems have been evaluated using equilibrium molecular dynamics simulation within the framework of Fumi–Tosi potential models. An expression for the thermal conductivity of binary ionic mixtures was derived from the phenomenological equations between flux densities and their conjugate forces in the related transport processes. Each transport coefficient was evaluated using the Green–Kubo formula. The statistical errors of thermal conductivity evaluated using six kinds of the coefficients in these mixtures were estimated to be ca. 7–12%, depending on composition, which is comparable with the case for single molten NaCl evaluated using three kinds of the coefficients. The calculation results for the equimolar mixture show that the thermal conductivity depends strongly on density, but only weakly on temperature. Furthermore, all the calculated thermal conductivities of the mixtures scale with m − 1/2 (N/V)2/3, where m is the average ionic mass and N/V is the number density. These results regarding temperature and density dependencies and scaling with m − 1/2 (N/V)2/3 are common to the previous results for a series of single molten alkali halides.