posted on 2020-09-29, 18:13authored byJyotishraj Thoudam, Tejas Mane, Dilip Sundaram
Molecular dynamics
simulations are conducted to investigate the
effect of melting on the energy accommodation coefficient (EAC) of
Al–noble gas systems. The accommodation coefficients are computed
for a gas temperature of 3000 K and slab temperatures in the range
of 600–1500 K. Three different noble gases, helium, argon,
and xenon, are considered. Density functional theory (DFT)-derived
gas–metal interatomic potentials are used to obtain accurate
predictions of accommodation coefficients. An abrupt jump in the accommodation
coefficient upon melting is observed for argon and xenon, whereas
the accommodation coefficient is negligibly affected for helium gas.
The effects of gas–metal potential and gas atom mass are probed
separately, and it is found that the gas–metal potential has
a negligible effect on the magnitude of EAC jumps. The gas atom mass,
on the other hand, exerted a strong effect; heavier gases exhibited
greater EAC jumps than lighter gases. The underlying physics is then
unraveled by studying the effects of surface roughness and lattice
dynamics on the accommodation coefficient. Surface roughness increases
the tangential EACs significantly for all gases, but the normal EACs
are not as strongly amplified. Analysis of the vibrational density
of states of solid and liquid slabs suggests the activation of low-frequency
vibrational modes upon melting. This coupled with the roughening of
surface upon melting results in an abrupt jump in the accommodation
coefficient, especially for heavier gases.