Giura Stefano, Schoen Martin
Stranski-Laboratorium für Physikalische und Theoretische Chemie, Fakultät für Mathematik und Naturwissenschaften, Technische Universität Berlin, Straße des 17. Juni 115, 10623 Berlin, Germany.
Stranski-Laboratorium für Physikalische und Theoretische Chemie, Fakultät für Mathematik und Naturwissenschaften, Technische Universität Berlin, Straße des 17. Juni 115, 10623 Berlin, Germany and Department of Chemical and Biomolecular Engineering, Engineering Building I, Box 7905, North Carolina State University, 911 Partners Way, Raleigh, North Carolina 27695, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Aug;90(2):022507. doi: 10.1103/PhysRevE.90.022507. Epub 2014 Aug 29.
We consider the phase behavior of a simple model of a liquid crystal by means of modified mean-field density-functional theory (MMF DFT) and Monte Carlo simulations in the grand canonical ensemble (GCEMC). The pairwise additive interactions between liquid-crystal molecules are modeled via a Lennard-Jones potential in which the attractive contribution depends on the orientation of the molecules. We derive the form of this orientation dependence through an expansion in terms of rotational invariants. Our MMF DFT predicts two topologically different phase diagrams. At weak to intermediate coupling of the orientation dependent attraction, there is a discontinuous isotropic-nematic liquid-liquid phase transition in addition to the gas-isotropic liquid one. In the limit of strong coupling, the gas-isotropic liquid critical point is suppressed in favor of a fluid- (gas- or isotropic-) nematic phase transition which is always discontinuous. By considering three representative isotherms in parallel GCEMC simulations, we confirm the general topology of the phase diagram predicted by MMF DFT at intermediate coupling strength. From the combined MMF DFT-GCEMC approach, we conclude that the isotropic-nematic phase transition is very weakly first order, thus confirming earlier computer simulation results for the same model [see M. Greschek and M. Schoen, Phys. Rev. E 83, 011704 (2011)].
我们通过修正平均场密度泛函理论（MMF DFT）以及巨正则系综中的蒙特卡罗模拟（GCEMC）来研究一种简单液晶模型的相行为。液晶分子间的成对加和相互作用通过 Lennard-Jones 势来建模，其中吸引作用依赖于分子的取向。我们通过旋转不变量展开推导这种取向依赖的形式。我们的 MMF DFT 预测了两种拓扑不同的相图。在取向依赖吸引的弱到中等耦合强度下，除了气 - 各向同性液相转变外，还存在一个不连续的各向同性 - 向列相液 - 液转变。在强耦合极限下，气 - 各向同性液临界点被抑制，转而支持一个总是不连续的流体 -（气或各向同性）- 向列相转变。通过在并行的 GCEMC 模拟中考虑三条代表性等温线，我们证实了 MMF DFT 在中等耦合强度下预测的相图的一般拓扑结构。从 MMF DFT - GCEMC 组合方法中，我们得出各向同性 - 向列相转变是非常弱的一级相变，从而证实了同一模型早期的计算机模拟结果 [见 M. Greschek 和 M. Schoen，《物理评论 E》83，011704（2011）]。
