CONSTANT-PRESSURE MOLECULAR-DYNAMICS SIMULATIONS OF THE CRYSTAL-SMECTIC TRANSITION IN SYSTEMS OF SOFT PARALLEL SPHEROCYLINDERS
CONSTANT-PRESSURE MOLECULAR-DYNAMICS SIMULATIONS OF THE CRYSTAL-SMECTIC TRANSITION IN SYSTEMS OF SOFT PARALLEL SPHEROCYLINDERS
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DOI：
10.1103/physreva.46.6541
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发表时间：
1992-11-15
影响因子：
2.9
通讯作者：
YONEZAWA, F
中科院分区：
文献类型：
--
作者：
AOKI, KM;YONEZAWA, F
为了研究晶体-近晶转变周围的热力学性质和微观结构，我们采用恒压分子动力学模拟方法，以软平行球柱为液晶模型。安徒生的方法[J.化学。太棒了。72,2384(1980)]以及Parrinello和Rahman的方法。莱特牧师。45,1196(1980)][45,1196(1980)][45,1196(1980)][45,1196(1980)][45,1196(1980)][45,1196(1980)][45,1196(1980)][45,1196(1980)][45,1196(1980)]应用于右平行六面体模拟盒，并对该模型的状态方程进行了计算。热力学性质，如热焓和体积随密度Rho*或温度的函数表现出明显的一级转变。垂直于分子轴的平面比面积的平方根L(垂直于分子轴)对Rho*的依赖关系显示出二维熔融的特征。我们计算了在分子轴方向上的比长度L(Z)，它对应于液晶区近晶层的厚度。从L(Z)和L(Z)/L(垂直-TO)的Rho依赖关系，我们证明了分子体积的各向异性在晶体-近晶转变中起着重要的作用。我们还观察到在这种转变前后扩散和结构性质都发生了明显的变化。垂直于取向方向的均方位移表明，在近晶相中，分子在层内自由扩散，尽管垂直于层的密度波在转变后仍然存在。
In order to investigate thermodynamic properties and microscopic structure around the crystal-smectic transition, we present constant-pressure molecular-dynamics simulations for soft parallel spherocylinders as a model for liquid crystals. The method of Andersen [J. Chem. Phys. 72, 2384 (1980)] as well as the method of Parrinello and Rahman [Phys. Rev. Lett. 45, 1196 (1980)] axe applied to a right parallelepiped simulation box, and the equation of state for this model is evaluated. Thermodynamic properties such as enthalpy and volume as functions of reduced density rho* or of temperature show a clear first-order transition. The dependence of l(perpendicular-to), the square root of the specific area of the plane perpendicular to the molecular axis, on rho* shows a feature characteristic of two-dimensional melting. We calculate the specific length l(z) in the direction of the molecular axis, which corresponds to the thickness of a smectic layer in the liquid-crystal region. From the rho* dependence of l(z) and l(z)/l(perpendicular-to), we show that the anisotropy of the molecular volume plays an important role in the crystal-smectic transition. We also observe a clear change in both diffusion and structural properties before and after this transition. The mean-square displacements in directions perpendicular to the alignment show that in the smectic phase the molecules diffuse freely within the layers, although the density wave in the direction perpendicular to layers does exist even after the transition.