First-Principles Informed Atomistic-Scale Calculations of Equilibrium Energy Accommodation Coefficients for Aluminum-Noble Gas Systems

Pinki and P Kulkarni and DS Sundaram, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 7182-7195 (2020).

DOI: 10.1021/acs.jpcc.9b11394

First-principles informed atomistic-scale simulations are conducted to compute equilibrium energy accommodation coefficients of aluminum-noble gas systems for a temperature range of 25-800 K. Density functional theory (DFT) derived gas-solid potential functions are employed to facilitate accurate predictions. Three different gases are considered: helium, argon, and xenon. Two different methods are employed to calculate accommodation coefficients: the parallel slab and single slab methods. In the parallel slab method, the gas is sandwiched between two parallel Al slabs and a temperature gradient is imposed. In the single slab method, the interaction between each gas atom and a slab is simulated separately, and over 10 000 such interactions are considered. The accommodation coefficients are generally lowest for helium and greatest for xenon. At a temperature of 300 K, the computed accommodation coefficients are 0.09, 0.27, and 0.34 for helium, argon, and xenon, respectively. The effect of temperature on accommodation coefficient is also studied, and new physical insights are offered to explain the temperature dependence of accommodation coefficient. Deficiencies and issues with classical models are identified. Contradictions and scatter in the experimental data are also resolved. Predictions agree reasonably well with the experimental data reported for smooth bare aluminum surfaces, but they exhibit poor agreement with other available experimental data reported for rough and passivated surfaces. The parallel slab method is found to be more effective for computing equilibrium accommodation coefficients.

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