arXiv subjects

F. Hirata

Publications and source records attributed to F. Hirata.

4 recordsLinked to original sources

arXiv2006

Statistical-mechanical theory of ultrasonic absorption in molecular liquids

We present results of theoretical description of ultrasonic phenomena in molecular liquids. In particular, we are interested in the development of microscopical, i.e., statistical-mechanical framework capable to explain the long living puzzle of the excess ultrasonic absorption in liquids. Typically, ultrasonic wave in a liquid can be generated by applying the periodically alternating external pressure with the angular frequency that corresponds to the ultrasound. If the perturbation introduced by such process is weak - its statistical-mechanical treatment can be done with the use of the linear response theory. We treat the liquid as a system of interacting sites, so that all the response/aftereffect functions as well as the energy dissipation and generalized (wave-vector and frequency dependent) ultrasonic absorption coefficient are obtained in terms of familiar site-site static and time correlation functions such as static structure factors or intermediate scattering functions. To express the site-site intermediate scattering functions we refer to the site-site memory equations in the mode-coupling approximation for the first-order memory kernels, while equilibrium properties such as site-site static structure factors, direct and total correlation functions are deduced from the integral equation theory of molecular liquids known as RISM or one of its generalizations. All the formalism is phrased in a general manner, hence the obtained results are expected to work for arbitrary type of molecular liquid including simple, ionic, polar, and non-polar liquids.

cond-mat.stat-mech↗

arXiv2005

Pressure dependence of diffusion coefficient and orientational relaxation time for acetonitrile and methanol in water: DRISM/mode-coupling study

We present results of theoretical description and numerical calculation of the dynamics of molecular liquids based on the Reference Interaction Site Model / Mode-Coupling Theory. They include the temperature-pressure(density) dependence of the translational diffusion coefficients and orientational relaxation times for acetonitrile and methanol in water at infinite dilution. Anomalous behavior, i.e. the increase in mobility with density, is observed for the orientational relaxation time of methanol, while acetonitrile does not show any deviations from the usual. This effect is in qualitative agreement with the recent data of MD simulation and with experimental measurements, which tells us that presented theory is a good candidate to explain such kind of anomalies from the microscopical point of view and with the connection to the structure of the molecules.

physics.chem-ph↗

arXiv2005

Study of anomalous mobility of polar molecular solutions by means of the site-site memory equation formalism

In this work, the memory equation approach is applied for theoretical study of dynamics of polar molecular liquids described by the interaction site model. The study includes the temperature-density(pressure) dependence of the translational diffusion coefficients D and orientational relaxation times t for infinitely dilute solutions of acetonitrile and methanol in water, and methanol in acetonitrile. Calculations are performed over the range of temperatures and densities employing the SPC/E model for water and optimized site-site potentials for acetonitrile and methanol. Despite an approximate character of the model potentials and closure relation used, the theory is able to reproduce qualitatively all main features of temperature and density dependences of D and t observed in computer and real experiments. In particular, anomalous behavior, i.e. the increase in mobility with density(pressure), is obtained for D and t of methanol in water, while acetonitrile in water or methanol in acetonitrile do not show deviations from the usual. The observed enhancement in the molecular mobility is interpreted in accordance with the concept by Yamaguchi et al. [J. Chem. Phys. 119 (2003) 1021], i.e. in terms of two competing origins of friction, which interplay with each other as density increases: the collisional and dielectric frictions that have tendency, respectively, to strengthen and weaken with increasing density.

physics.chem-ph↗

arXiv2005

Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: acetonitrile in water, methanol in water, and methanol in acetonitrile

We present results of theoretical study and numerical calculation of the dynamics of molecular liquids based on combination of the memory equation formalism and the reference interaction site model - RISM. Memory equations for the site-site intermediate scattering functions are studied in the mode-coupling approximation for the first order memory kernels, while equilibrium properties such as site-site static structure factors are deduced from RISM. The results include the temperature-density(pressure) dependence of translational diffusion coefficients D and orientational relaxation times t for acetonitrile in water, methanol in water and methanol in acetonitrile, all in the limit of infinite dilution. Calculations are performed over the range of temperatures and densities employing the SPC/E model for water and optimized site-site potentials for acetonitrile and methanol. The theory is able to reproduce qualitatively all main features of temperature and density dependences of D and t observed in real and computer experiments. In particular, anomalous behavior, i.e. the increase in mobility with density, is observed for D and t of methanol in water, while acetonitrile in water and methanol in acetonitrile do not show deviations from the ordinary behavior. The variety exhibited by the different solute-solvent systems in the density dependence of the mobility is interpreted in terms of the two competing origins of friction, which interplay with each other as density increases: the collisional and dielectric frictions which, respectively, increase and decrease with increasing density.

physics.chem-ph↗