密度泛函理论对受限流体导数热力学性质的预测
Density Functional Theory Predictions of Derivative Thermodynamic Properties of a Confined Fluid
AI总结：
本文利用DFT方法预测受限流体的导数热力学性质，通过参数调整和分子模拟验证了等温压缩性和热膨胀系数的计算结果。
摘要：
纳米孔中的流体对许多工程应用具有重要意义，包括超级电容器中的能量存储、非常规源中石油的回收或海水淡化。受限于纳米孔的流体热力学性质与相同流体在本体中的性质不同。密度泛函理论（DFT）已被广泛用于建模受限流体的热力学性质。然而，它很少用于导数热力学性质的计算。在这里，我们使用了一个相对简单的基于Percus-Yevick方程的氩气DFT模型，并表明使用标准参数化时，它无法预测导数性质。然而，对参数进行轻微调整可实现选定温度下的等温压缩性和热膨胀系数的定量预测。使用调整后的参数化，我们计算了受限于不同尺寸碳狭缝孔的氩气压缩性，并证明了在受限条件下氩气的压缩性低于本体，并且与孔隙尺寸相关。我们通过蒙特卡罗分子模拟验证了DFT的预测。除了等温压缩性，我们还计算了受限氩气的热膨胀系数。我们的计算表明，它与压缩性相似——它始终低于本体值，并且对于较小的孔隙尺寸逐渐增加。对于几种选定的孔隙尺寸，我们通过蒙特卡罗模拟验证了DFT的计算。总体而言，我们的结果表明，经典DFT可以用于计算受限流体的导数热力学性质，而使用分子模拟预测这些性质在计算上具有挑战性。
英文摘要：
Fluids in nanopores are of importance for many engineering applications, including energy storage in supercapacitors, hydrocarbons recovery from unconventional sources, or water desalination. Thermodynamic properties of fluids confined in nanopores differ from the properties of the same fluids in bulk. Density functional theory (DFT) has been widely used for modeling thermodynamics of confined fluids. However, it is rarely used for calculations of derivative thermodynamic properties. Here we use a rather simple DFT model for argon based on the Percus-Yevick equation, and showed that with standard parametrization it fails to predict derivative properties. However, slight adjustment in parameters leads to quantitative predictions of isothermal compressibility and thermal expansion coefficient at a selected temperature. Using the adjusted parameterization we performed the calculations of compressibility of argon confined in carbon slit pores of various sizes, and demonstrated that the compressibility of argon in confinement is lower than that in bulk and is pore size dependent. We confirmed the DFT predictions using the Monte Carlo molecular simulations. In addition to isothermal compressibility, we calculated the thermal expansion coefficient of confined argon. Our calculations showed that it behaves similar to compressibility -- it is always lower than the bulk value and gradually increases for smaller pore sizes. For several selected pore sizes we verified the DFT calculations by Monte Carlo simulations. Overall, our results suggest that the classical DFT can be utilized for calculations of derivative thermodynamic properties of confined fluids, which are computationally challenging to predict using molecular simulations.
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