Statistical mechanics of simple coulomb systems

The phase diagram and dynamical properties of systems of particles interacting through a repulsive screened Coulomb (Yukawa) potential have been calculated using molecular and lattice dynamics techniques. The phase diagram contains both a melting transition and a transition from fcc to bcc crystalline phases. These phase transitions have been studied as a function of potential shape (screening length) and compared to phenomenological criteria for transition temperatures such as those of Lindemann and of Hansen and Verlet. The transition from fcc to bcc with increasing temperature is shown to result from a higher entropy in the bcc phase because of its softer shear modes. Even when the stable solid phase below the melting temperature is fcc, bcc‐like local order is found in the liquid phase. This may substantially slow crystallization. The calculated phase diagram and shear modulus are in good agreement with experiments on colloidal suspensions of polystyrene spheres. The single particle dynamics of Yukawa systems show several unusual features. There is a pronounced subdiffusive regime in liquids near and below the melting temperature. This regime reflects the existence of two time scales: a typical phonon period, and the time for a particle to feel a new environment. The second time scale becomes longer as the temperature is lowered or the range of interaction (screening length) increases.

Phase diagram and dynamics of Yukawa systems

Statistical physics of dense plasmas: Thermodynamics, transport coefficients and dynamic correlations

Hydrogen and helium are the most abundant elements in the Universe. They are also, in principle, the most simple. Nonetheless, they display remarkable properties under extreme conditions of pressure and temperature that have fascinated theoreticians and experimentalists for over a century. Advances in computational methods have made it possible to elucidate ever more of their properties. Some of these methods that have been applied in recent years, in particular, those that perform simulations directly from the physical picture of electrons and ions, such as density functional theory and quantum Monte Carlo are reviewed. The predictions from such methods as applied to the phase diagram of hydrogen, with particular focus on the solid phases and the liquid-liquid transition are discussed. The predictions of ordered quantum states, including the possibilities of a low- or zero-temperature quantum fluid and high-temperature superconductivity are also considered. Finally, pure helium and hydrogen-helium mixtures, the latter which has particular relevance to planetary physics, are discussed.

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The properties of hydrogen and helium under extreme conditions

A semi-empirical `universal' corresponding-states relationship, for the dimensionless transport coefficients of dense fluids as functions of the reduced configurational entropy, was proposed more than twenty years ago and established by many simulations. Here it is shown analytically, by appealing to Enskog's original results for the inverse-power potentials, that the quasi-universal entropy scaling can be extended also to dilute gases. The analytic form and the possible origin for the entropy scaling for dense fluids are discussed in view of this unexpected result. On the basis of the entropy scaling we predict a minimum in the shear viscosity as a function of temperature for all soft inverse-power potentials, in quantitative agreement with the available simulations.

https://iopscience.iop.org/article/10.1088/0953-8984/11/28/303/pdf

A quasi-universal scaling law for atomic transport in simple fluids

Statistical mechanics of dense ionized matter. III. Dynamical properties of the classical one-component plasma

We present molecular-dynamics computations of the velocity autocorrelation function and the dynamical structure factor of the classical one-component plasma. At high densities, the former exhibits marked oscillations, whereas the latter consists of very sharp peaks near the plasma frequency, up to wave vectors of order $\frac{1}{a}$, where $a$ is the ion-sphere radius. The resulting dispersion curve is discussed.

E.L. Pollock

Papers

Statistical mechanics of dense ionized matter. III. Dynamical properties of the classical one-component plasma

Velocity autocorrelation function and dynamical structure factor of the classical one-component plasma