Abstract
The characteristics of atomic-scale mixing are determined by diffusive processes driven by gradients. One such process is interdiffusion, a process driven by density gradients. We consider the various options for formulating interdiffusion in terms of Green–Kubo autocorrelation functions and the thermodynamic factor. Through models for the direct correlation function, we generalize expressions for the thermodynamic factor to include different electron and ion temperatures, electron degeneracy, finite-temperature exchange, and strong coupling. Additionally, a Gaussian autocorrelation function (GAF) is employed for a binary ionic mixture, yielding a simple analytic transport model for interdiffusion. The GAF model is shown to be accurate for moderately and strongly coupled plasmas.
Highlights
Interdiffusion, which is atomic-scale mixing driven by density gradients, occurs in extremely disparate physical systems
We consider the various options for formulating interdiffusion in terms of Green–Kubo autocorrelation functions and the thermodynamic factor
The thermodynamic factor can be obtained from integral equation theory, which gives the radial distribution functions[26] as gii[0] ðrÞ 1⁄4 exp ðÀbuii[0] ðrÞ þ hii[0] ðrÞ À cii[0] ðrÞ þ Bii[0] ðrÞÞ; (28)
Summary
Interdiffusion, which is atomic-scale mixing driven by density gradients, occurs in extremely disparate physical systems. Interdiffusion controls the distribution of elements throughout a star, impacting its evolution.[10,11,12] diffusive mixing of thermonuclear fuel in inertial confinement fusion experiments[13] can spoil the burn conditions through radiative losses.[14,15,16,17,18] Recent large-scale molecular dynamics (MD) simulations[19] of heated plasma interfaces have exposed many complex issues: multiple ionic temperatures, jetting of light particles across interfaces uncoupled velocity fields, and intense electric fields Experimental data for these processes are minimal but have motivated several current experiments.[20,21,22,23,24]. In most computational studies of interdiffusion, the thermodynamic factor is set to unity.[26–29] While this may be accurate in some cases,[5] a complete exploration across physical regimes for a wide range of mixtures is lacking. We compare this result to MD data, revealing excellent agreement in moderately and strongly coupled regimes
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