Mognetti B M, Yelash L, Virnau P, Paul W, Binder K, Müller M, MacDowell L G
Institut für Physik, Johannes Gutenberg-Universität, Mainz, Staudinger Weg 7, Mainz, Germany.
J Chem Phys. 2008 Mar 14;128(10):104501. doi: 10.1063/1.2837291.
Monte Carlo simulations are presented for a coarse-grained model of real quadrupolar fluids. Molecules are represented by particles interacting with Lennard-Jones forces plus the thermally averaged quadrupole-quadrupole interaction. The properties discussed include the vapor-liquid coexistence curve, the vapor pressure along coexistence, and the surface tension. The full isotherms are also accessible over a wide range of temperatures and densities. It is shown that the critical parameters (critical temperature, density, and pressure) depend almost linearly on a quadrupolar parameter q=Q(4)T, where Q* is the reduced quadrupole moment of the molecule and T* the reduced temperature. The model can be applied to a variety of small quadrupolar molecules. We focus on carbon dioxide as a test case, but consider nitrogen and benzene, too. Experimental critical temperature, density, and quadrupolar moment are sufficient to fix the parameters of the model. The resulting agreement with experiments is excellent and marks a significant improvement over approaches which neglect quadrupolar effects. The same coarse-grained model was also applied in the framework of perturbation theory in the mean spherical approximation. As expected, the latter deviates from the Monte Carlo results in the critical region, but is reasonably accurate at lower temperatures.
本文给出了真实四极流体粗粒化模型的蒙特卡罗模拟。分子由与 Lennard-Jones 力相互作用的粒子以及热平均四极 - 四极相互作用来表示。所讨论的性质包括气液共存曲线、共存时的蒸气压以及表面张力。在很宽的温度和密度范围内也能得到完整的等温线。结果表明，临界参数（临界温度、密度和压力）几乎线性地依赖于四极参数 q = Q(4)T，其中 Q是分子的约化四极矩，T是约化温度。该模型可应用于多种小分子四极分子。我们将二氧化碳作为一个测试案例重点研究，但也考虑了氮气和苯。实验得到的临界温度、密度和四极矩足以确定模型的参数。与实验结果的一致性非常好，这标志着相对于忽略四极效应的方法有了显著改进。同样的粗粒化模型也应用于平均球近似下的微扰理论框架中。正如预期的那样，后者在临界区域偏离了蒙特卡罗结果，但在较低温度下相当准确。
