Equation of state of argon : experiments on Z, density functional theory (DFT) simulations, and wide-range model.

Abstract

Over the last few years, first-principles simulations in combination with increasingly accurate shock experiments at multi-Mbar pressure have yielded important insights into how matter behaves under shock loading. Noble gases like argon are particularly interesting to study as a model system due to the closed shell electronic structure that results in a weak interatomic interaction at normal conditions followed by pronounced ionization and strong interaction under compression. Cryogenic argon is also optically transparent while shocked argon is metallic, displaying a reflective shock front, thus allowing for shock velocity measurement to very high precision. In this report, we present experimental results for shock compression of liquid cryogenic argon to several Mbar using magnetically accelerated flyers on the Z machine, first-principles simulations based on Density Functional Theory, and an analysis of tabular equations of state (EOS) for argon, including a newly developed wide-range EOS model. 3 AcknowledgmentWe sincerely thank the many devoted specialists with Z-Operations who are involved in planning and executing experiments on the Z-machine. We thank the cryogenic team: Andrew Lopez, Keegan Shelton, and Jose Villalva for installing and running the cryostat. We thank Aaron Bowers, Nicole Cofer, and Jesse Lynch for assembling the cryo-targets. We thank Charlie Meyers for running the VISAR diagnostics and Devon Dalton for handling target design.4

High-pressure, high-temperature molecular doping of nanodiamond

“…The nanodiamond grain sizes ranged from 1 -200 nm (Fig. S2), indicating that significant carbon diffusion occurs during HPHT synthesis, which was likely enhanced by the high synthesis temperatures that surpass the melting point of argon at 20 GPa (1580 K) (18). The carbon K-edge EELS spectra of pure diamond has a characteristic near-edge structure with prominent σ * peak at 290 eV a dip at 302.5 eV (19).…”

An efficient approach to ab initio Monte Carlo simulation

“…Our method yields 40-70% acceptance of N-particle moves at a mean per-particle displacement of 1.0Å in dense argon; this figure is at least an order of magnitude larger than in Ref. 31 Errors on the mean were calculated as described in the text and are smaller than the symbol sizes. for shortcomings in the reference potential through correspondingly greater enhancements of acceptance probability.…”

Photothermal effects during nanodiamond synthesis from a carbon aerogel in a laser-heated diamond anvil cell

“…While increasing the heating irradiance to 17 MW/cm 2 , the average carbon aerogel temperature increased monotonically up to 1340 K ( Fig. 2), below the melting point of argon (1383 K at 16.3 GPa [34]). At these irradiances, the temperature remained relatively constant throughout heating (within one standard deviation of the average temperature), and no nanodiamond formation was observed.…”

“…S5), which has a well-documented pressure dependence [33]. During compression to 16.3 GPa, the argon pressure medium undergoes a phase transition to solid, facecentered cubic argon [34]. In addition, higher laser irradiances were chosen to ensure similar synthesis temperatures.…”