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In rarefied gas flows, accommodation coefficients (ACs) serve as core parameters for gas-surface interactions and play a crucial role in the accuracy of mesoscopic model simulations. However, there exist significant discrepancies in the ACs obtained by different molecular dynamics simulation methods. To accurately characterize the momentum and energy accommodation properties of rarefied gases with solid surfaces under non-equilibrium conditions, this study systematically investigates the gas-surface interactions between argon molecules and platinum surfaces using molecular dynamics (MD) methods. By employing single scattering (SS) and continual scattering (CS) approaches, the influence of gas-gas collisions on tangential momentum accommodation coefficients (TMAC), normal momentum accommodation coefficients (NMAC), and energy accommodation coefficients (EAC) is comparatively analyzed, along with the operational laws of parameters such as surface morphology, surface temperature, incident velocity, and mean free path (MFP). The results demonstrate that gas density exerts a dual effect on momentum and energy accommodation: at smaller MFP, the high gas density within the interaction region impedes the accommodation of subsequent incident molecules with the surface, resulting in lower ACs; at moderate MFP, gas-gas collisions promote accommodation by increasing the frequency of gas-surface collisions, thereby enhancing ACs. Within the MFP range of 2.0–60.0 nm, the deviation in ACs between the CS and SS methods ranges from –14.88% to 5.21%, validating the dual role of gas density. Furthermore, at larger MFP, the TMAC and NMAC obtained via the CS method exhibit different trends with increasing MFP across surfaces of varying morphologies. In contrast to gas density, increases in both surface temperature and incident velocity shorten the interaction time, leading to reduced ACs. Notably, the effect of temperature varies across surfaces with different morphologies: elevated temperatures on smooth surfaces enhance the thermal fluctuations of surface atoms, thereby increasing NMAC, while elevated temperatures on rough surfaces cause smoothing of rough structures, thus inhibiting accommodation. Under high-speed incident conditions, gas-gas collisions promote NMAC on smooth surfaces, inhibit both TMAC and NMAC on rough surfaces, and suppress EAC across all surfaces. Additionally, the ACs obtained via both the CS and SS methods decrease with increasing incident velocity across surfaces of different morphologies.
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Keywords:
- molecular dynamics /
- gas-surface interaction /
- accommodation coefficient /
- surface morphology
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图 1 模拟盒子示意图
Figure 1. MD simulation box schematic.
图 2 气体分子入射角度示意图
Figure 2. Schematic diagram of the incident angle of gas molecules.
图 3 不同粗糙形态表面示意图 (a) 1D正弦粗糙表面; (b) 2D正弦粗糙表面; (c) 金字塔形粗糙表面; (d) 随机粗糙表面
Figure 3. Schematic diagrams of surfaces with different roughness morphologies: (a) 1D sinusoidal rough surface; (b) 2D sinusoidal rough surface; (c) pyramidal rough surface; (d) random rough surface.
图 4 光滑表面下CS与SS方法ACs随样本量的变化 (a) SS方法; (b) CS方法
Figure 4. Variation of ACs with sample size for CS and SS methods on a smooth surface: (a) SS method; (b) CS method.
图 6 不同形态表面下CS方法随MFP变化得到的ACs与SS方法的ACs对比 (a) 光滑表面; (b) 2D正弦粗糙表面; (c) 随机粗糙表面
Figure 6. Comparison of ACs obtained by the CS method with varying MFP and by the SS method on surfaces with different morphologies: (a) smooth surface; (b) 2D sinusoidal rough surface; (c) random rough surface.
图 7 不同形态表面和MFP下的平均气体-表面相互作用时间
Figure 7. Average gas-surface interaction time on surfaces with different morphologies at varying MFP.
图 8 不同形态表面和MFP下气体分子的吸附概率
Figure 8. Sticking probability of gas molecules on surfaces with different morphologies at varying MFP.
图 9 不同形态表面和表面温度下CS与SS方法得到的ACs对比图 (a) 光滑表面; (b) 1D正弦粗糙表面; (c) 2D正弦粗糙表面; (d) 金字塔形粗糙表面; (e) 随机粗糙表面
Figure 9. Comparison of ACs obtained by CS and SS methods on surfaces with different morphologies at varying surface temperatures: (a) smooth surface; (b) 1D sinusoidal rough surface; (c) 2D sinusoidal rough surface; (d) pyramidal rough surface; (e) random rough surface.
图 10 不同形态表面下CS与SS方法吸附概率随表面温度的变化
Figure 10. Variation of sticking probabilities for CS and SS methods with surface temperature on surfaces with different morphologies.
图 11 光滑及2D正弦粗糙表面下CS与SS方法平均气体-表面相互作用时间随表面温度的变化
Figure 11. Variation of average gas-surface interaction time with surface temperature for CS and SS methods on smooth and 2D sinusoidal rough surfaces.
图 12 CS方法入射气体分子的典型碰撞轨迹图
Figure 12. Typical collision trajectories of incident gas molecules under the CS method.
图 13 不同形态表面和入射速度下CS与SS方法得到的ACs对比图 (a) 光滑表面; (b) 1D正弦粗糙表面; (c) 2D正弦粗糙表面; (d) 金字塔形粗糙表面; (e) 随机粗糙表面
Figure 13. Comparison of ACs obtained by CS and SS methods on surfaces with different morphologies at varying incident velocities: (a) smooth surface; (b) 1D sinusoidal rough surface; (c) 2D sinusoidal rough surface; (d) pyramidal rough surface; (e) random rough surface.
图 14 光滑表面YOZ平面势能分布示意图
Figure 14. Schematic diagram of potential energy distribution in the YOZ plane on a smooth surface.
图 15 不同形态表面和入射速度下CS与SS方法的平均气体-表面相互作用时间
Figure 15. Average gas-surface interaction time for CS and SS methods on surfaces with different morphologies at varying incident velocities.
图 16 不同入射速度下光滑表面CS与SS方法的总气-固碰撞次数和平均单次碰撞能量损失值
Figure 16. Total gas-solid collision counts and average energy loss per collision for CS and SS methods on a smooth surface at varying Incident velocities.
图 17 不同形态表面和入射速度下CS与SS方法的ACs的相对偏差平均值
Figure 17. Average relative deviations of ACs between CS and SS methods on surfaces with different morphologies at varying incident velocities.
表 1 光滑表面下MFP为2.0、1.0、0.5、0.2 nm时得到的ACs
Table 1. Accommodation coefficients obtained on a smooth surface at MFP equal to 2.0, 1.0, 0.5, and 0.2 nm.
MFP/nm TMAC NMAC EAC 2.0 0.669 0.533 0.538 1.0 0.637 0.446 0.498 0.5 0.612 0.408 0.425 0.2 0.491 0.269 0.278 
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表 2 不同形态表面和MFP下CS与SS方法ACs的正负最大差值
Table 2. Maximum positive and negative differences in ACs between CS and SS methods on surfaces with different morphologies at varying MFP.
表面形态 正负最大差值 TMAC NMAC EAC Smooth 正差值 0.007 0.002 0.028 负差值 –0.028 –0.070 –0.004 2Dsin 正差值 0.020 0.024 0.018 负差值 –0.143 –0.052 –0.013 Random 正差值 0.018 0.017 0.017 负差值 –0.064 –0.080 –0.022
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表 3 不同形态表面下SS方法在300 K和900 K表面温度得到的ACs的差值
Table 3. Differences in ACs obtained by the SS method on surfaces with different morphologies at surface temperatures of 300 K and 900 K.
表面形态 TMAC NMAC EAC Smooth 0.213 0.009 0.140 1Dsin 0.325 0.124 0.270 2Dsin 0.335 0.141 0.249 Pyramid 0.286 0.107 0.226 Random 0.236 0.111 0.224
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