Numerical calculation of the dielectric relaxation time distribution function in polar liquids

A numerical method for calculation of the relaxation time distribution function based on the discrete Fourier transform of the dispersion part of the complex dielectric permittivity is developed. The time relaxation distribution function is found for water; its dispersion of relaxation times is narrow. This is explained by the presence of distorted hydrogen bonds (the Pople model).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 37–40, March, 1982.     

Computer simulation of ionic systems. Influence of boundary conditions

The results of molecular dynamics calculations for systems of charged particles under periodic boundary conditions are reported for the case in which the periodic array of particles makes a macroscopically large sphere surrounded by a continuum of dielectric constant ?′. It is shown that thermodynamic and most dynamic properties are independent of the nature of the surrounding medium. The conductivity σ(ω) of the system depends strongly on the dielectric properties of the surrounding medium.     

Plasmon modes at a wedge using a non-local dielectric function

Plasmon modes at a wedge have been obtained by using a non-local dielectric function. It is shown that the effect of this dielectric function is roughly equivalent to rounding the edge of the wedge but using a local dielectric function.     

Calculation of the dielectric function for highly excited polar semiconductors

The optical dielectric function of an electron-hole plasma in highly excited polar semiconductors with a direct band gap is calculated by solving a Bethe-Salpeter equation for the polarization function. The screening of the Coulomb potential is treated in a damped phonon-plasmon-pole approximation. We include the complex dynamical self-energy corrections as well as electron-hole correlations.Project of the Sonderforschungsbereich Frankfurt/Darmstadt, financed by special funds of the Deutsche Forschungsgemeinschaft     

Quasiclassical boundary conditions for Fermi liquids at surfaces

The general boundary conditions at surfaces are derived within the quasiclassical theory of superfluidity in Fermi liquids (superconductors, superfluid³He). These conditions supplement the transport-like equations first introduced into the theory of superconductivity by G. Eilenberger, and allow a quantitative analysis of superfluids near a wall.     

Formation of associates of solvated cations in salt solutions in polar dielectric liquids

Experimental results are presented on excitation of oscillations of polarization charges of solvated ions in an aqueous solution of a mixture of cerium and lead nitrates under an external asymmetric electric field and the directed motion of solvated cerium and lead cations, caused by this process. The applicability of the approximation of the existence of a self-consistent electric field in the solution volume to explain the observed frequency ranges of the manifestation of the effect of electroinduced selective drift of solvated cations is demonstrated. The results of a theoretical analysis of the possibility of forming associates from solvated ions are presented.     

Anisotropic dielectric function in polar nanoregions of relaxor ferroelectrics

The Letter suggests treating the infrared reflectivity spectra of single crystal perovskite relaxors as fine-grained ferroelectric ceramics: locally frozen polarization makes the dielectric function strongly anisotropic in the phonon frequency range and the random orientation of the polarization at nanoscopic scale requires taking into account the inhomogeneous depolarization field. Employing a simple effective medium approximation (the Bruggeman symmetrical formula) turns out to be sufficient for reproducing all principal features of room temperature reflectivity of Pb(Mg(1/3)Nb(2/3))O3. One of the reflectivity bands is identified as a geometrical resonance entirely related to the nanoscale polarization inhomogeneity. The approach provides a general guide for systematic determination of the polar mode frequencies split by the inhomogeneous polarization at the nanometer scale.     

Influence of inertia on the dielectric properties of polar liquids. Application to deoxyhemoglobin S

In this paper, we have derived oscillator relations, including inertial effects, which are an extension of the Debye relations, and have shown their interest together with their limits of application. These relations may be applied as soon as the dimensionless damping parameter γ is less than 10, and yield a lot of information on the molecular structure of the medium. We have used them in the study of an abnormal hemoglobin, termed deoxyhemoglobin S, from experimental data of dielectric constants obtained by Delalic et al. Our calculation is based upon the Kramers-Kronig method. By means of a best-fit procedure of the dispersion plots together with the Cole-Cole plots, the presence of a monomeric phase and of three main aggregates which are well characterized, is found. So, we get several stereotypes of the medium, and its time evolution is interpreted in terms of molecular parameters. We calculate the moment of inertia of these aggregates and we give the evolution of the friction coefficient ξ. We remark that the decrease of γ corresponds to an ordered array of the medium and that its limiting value equal to 1.6 is related to a gel state, in full agreement with the theoretical estimate obtained by Coffey.     

Theory of polar liquids

Two recent contributions to the statistical theory of polar fluids, namely the perturbation theory of Stell, Rasaiah and Narang (SRN) and the meanspherical-approximation (MSA) results of Wertheim, and of Nienhuis and Deutch, are compared and contrasted for the conceptually simple model of hard spheres, diameter R, with central point dipoles, of strength μ (dipolar hard spheres). It is shown that the MSA approach replaces correlation functions which enter correctly into the SRN theory by their low-density limits : to this extent it is unsatisfactory. On the other hand the MSA work does suggest reasons why the naive Padé approximant featuring in SRN theory may be expected to do reasonable justice to the physics of the problem. Numerical comparisons of the excess free-energy (as compared with non-polar hard spheres) as a function of reduced density, ρ* = ρR ³, are given at two temperatures, T* = 2 and T* = 0·25, where T* = kTR ³/μ². Similar curves, for T* = 1 and T* = 0·5, are available from the authors. The gas-liquid (T*, ρ*)-phase boundary is located, near the critical point, on both theories, as are the vapour pressure curves. These are calculated using the Carnahan-Starling equation of state for hard spheres ; and critical comment is made in justification of employing this in the context of MSA results for the excess quantities. The two theories are found to have appreciably different numerical consequences.     

Quasi-one-dimensional structure of polar liquids

The model of hindered molecular rotation considers a dense polar liquid as an infinite statistical chain of particles bound by dipole forces. The applicability limits of this quasi-one-dimensional model and the nature of possible phase transitions in the system under consideration are discussed.     

不同温度下复杂介质结构内带电规律仿真分析

卫星上某些介质结构会遭遇较大范围的温度变化, 其电导率会随之出现数量级的变化, 这将显著影响内带电结果. 受限于电导率-温度模型和内带电三维仿真工具, 该温度效应远没有得到深入研究. 为此, 在真空变温(253-353 K)和强电场(MV/m量级)条件下测试了某种星用改性聚酰亚胺介质的电导率, 借鉴Arrhenius电导率-温度模型并考虑强电场下电导率的增强效应, 发现电导活化能取值为0.40 eV时, 可得到良好的拟合结果. 在此基础上, 同时考虑辐射诱导电导率, 采用地球同步轨道恶劣电子辐射能谱, 对该类介质盘环结构进行内带电三维仿真, 发现其内带电程度随温度降低而显著增加, 带电最严重的区域位于靠近辐射源的接地面边线. 温度低于250 K时, 2 mm屏蔽铝板下该区域的场强可达到10⁷ V/m量级, 发生介质击穿放电的可能性较大. 所讨论的电导率-温度模型与内带电三维建模方法对进一步评估卫星介质结构内带电程度和做好防护设计具有重要参考意义.     

Molecular dynamics calculation of the dielectric constant without periodic boundary conditions. I

We outline the difficulties in obtaining a reliable value of the dielectric constant of a fluid using molecular dynamics calculations with periodic boundary conditions, and give some explanation of the observed asymptotic behaviour of h_D (r) and hΔ(r) in Monte Carlo simulations of dipolar hard spheres. An alternative method consisting in simulating a dielectric in vacuum is described. This is applied to two dimensional systems. The pertinent theoretical relations for a dielectric disc in vacuum are therefore derived. It is concluded that relations involving MC or MD computation of <m ²> must be carefully handled.     

A simple capacitive cell for the measurement of liquids dielectric constant under transient thermal conditions

A simple device for the measurement of the complex dielectric permittivity of liquids in various thermodynamic states has been developed. It uses a cylindrical aluminium capacitor of a type currently applied in tuning antenna circuits. The capacitor is filled with the liquid solution under study. A comparison of its capacity is made with that of the nitrogen filled capacitor tested under the same thermal conditions. This comparison allows the determination of the real and imaginary part of the solutions permittivity as a function of temperature (between 150 and 300 K) and frequency (between 100 Hz to 2 MHz). After validating the technique with pure glycerol and pure 1,2-propanediol, spectroscopic measurements have been undertaken on pure and diluted 1,2-propanediol in water. Due to the low heat capacity and the high thermal conductivity of the capacitor, cooling rates of 40 K/min have been achieved inside the solution, allowing measurements in the supercooled liquid and vitreous states. Results are presented and discussed in terms of relaxation and the physical states of the sample. By selecting the required thermal conditions, this device permits the observation of thermal transitions, such as ice crystallisation, and measurements to be conducted in the unstable supercooled liquid state. These measurements are necessary in the development of an effective electromagnetic warming device for vitrified cryoprotective solutions.     

Electromagnetodynamics of polar liquids and suspensions

We study electric and magnetic effects on the dynamics of polar liquids and of fluid suspensions of particles carrying electric and/or magnetic dipole moments. The hydrodynamic equations of motion are discussed in detail and compared with equations proposed in the literature. We derive simplified equations valid on a slow timescale.     

Computer simulation of vacancy migration in a fcc tilt boundary

Vacancy jumps in a bicrystal model of Σ = 5 (36.9°) [001] tilt boundary in aluminum have been observed at temperatures between 700 and 800 K by means of molecular dynamics simulation. Preliminary results indicated considerable structure dependence and yielded an activation energy for vacancy migration of 0.38 eV. In contrast to a previous study of vacancy migration in a bcc tilt boundary, thermal activation of a boundary interstitial by Frenkel pair production was not observed.