Inquiry into thermodynamic behavior of hard sphere plus repulsive barrier of finite height
Inquiry into thermodynamic behavior of hard sphere plus repulsive barrier of finite height
复制标题
硬球加有限高度排斥势垒的热力学行为探讨
DOI：
10.1063/1.3265984
复制
发表时间：
2009-11-28
影响因子：
4.4
通讯作者：
Solana, J. R.
中科院分区：
文献类型：
--
作者：
Zhou, Shiqi;Solana, J. R.
提出了一种桥函数近似方法，以闭合具有纯排斥势流体的奥恩斯坦 - 泽尼克（OZ）积分方程。随后，通过将该近似方法应用于两种排斥势，即方肩势和三角肩势，来检验桥函数近似的性能。在较宽的流体相密度范围和多个温度下，对模拟结果与OZ方法进行了广泛比较。结果发现，在温度不太低时，两种方法的一致性极佳；在极低温度下，一致性也令人满意。接着，利用这种整体可信度较高的OZ方法，研究液相反常现象（即在低温下的液 - 液相转变以及相图特定区域内热膨胀系数为负值的现象）是否可能存在。虽然此前传统的一阶热力学微扰理论（TPT）已预测方肩势中存在液相反常现象，但本研究表明，在OZ方法中液 - 液相转变消失了，因此一阶TPT的预测仅仅是由于该理论在低温下的局限性所导致的假象。然而，OZ方法确实预测出了负的热膨胀系数。本文提出的桥函数近似方法无需可调参数，适用于近期提出的非硬球微扰方案。
A bridge function approximation is proposed to close the Ornstein-Zernike (OZ) integral equation for fluids with purely repulsive potentials. The performance of the bridge function approximation is then tested by applying the approximation to two kinds of repulsive potentials, namely, the square shoulder potential and the triangle shoulder potential. An extensive comparison between simulation and the OZ approach is performed over a wide density range for the fluid phase and several temperatures. It is found that the agreement between the two routes is excellent for not too low temperatures and satisfactory for extremely low temperatures. Then, this globally trustworthy OZ approach is used to investigate the possible existence or not of a liquid anomaly, i.e., a liquid-liquid phase transition at low temperatures and negative values of the thermal expansion coefficient in certain region of the phase diagram. While the existence of the liquid anomaly in the square shoulder potential has been previously predicted by a traditional first-order thermodynamic perturbation theory (TPT), the present investigation indicates that the liquid-liquid phase transition disappears in the OZ approach, so that its prediction by the first-order TPT is only an artifact originating from the low temperature inadequacy of the first-order TPT. However, the OZ approach indeed predicts negative thermal expansion coefficients. The present bridge function approximation, free of adjustable parameters, is suitable to be used within the context of a recently proposed nonhard sphere perturbation scheme.