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首页> 外文期刊>The Journal of Chemical Physics >A comparison of quasi-harmonic lattice dynamics and Monte Carlo simulation of polymeric crystals using orthorhombic polyethylene
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A comparison of quasi-harmonic lattice dynamics and Monte Carlo simulation of polymeric crystals using orthorhombic polyethylene

机译：正交晶体聚乙烯的准谐波晶格动力学比较和蒙特卡罗模拟

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摘要

The temperature dependence of lattice parameters, elastic constants and other physical properties of crystalline polyethylene at zero pressure in the orthorhombic phase is discussed. Two complementary approaches, self-consistent quasi-harmonic lattice dynamics and Monte Carlo simulation, both of which are predicated on the use of empirical force fields to describe the interatomic potentials, are critically compared. Both techniques are studied in their classical and quantum mechanical versions, to assess the accuracy and limitations of each method. Particular attention is paid to the classical approximation, the onset of anharmonicities in dynamical behavior which are not captured by the quasi-harmonic approximation, and finite size effects. It is shown that quantum effects are important throughout the range of temperatures 0 less than or equal to T less than or equal to 300 K. At temperatures below about 2/3 of the melting temperature (i.e., 250 K for polyethylene) the two approaches yield consistent results in both classical and quantum mechanical cases for a given empirical force field, provided that finite size effects are avoided. Above 300 K, anharmonic effects become quite pronounced. The combined treatment of these effects in the framework of path integral Monte Carlo (PIMC) pushes the limits of current computational feasibility, due to simulation sizes required. Guidelines are offered for choosing between classical simulations, quasi-harmonic methods, and full path integral Monte Carlo simulation. (C) 1998 American Institute of Physics. [References: 43]
机译：讨论了斜方晶相在零压力下晶态聚乙烯的晶格参数，弹性常数和其他物理性能的温度依赖性。严格地比较了两种互补方法，即自洽准谐波晶格动力学和蒙特卡罗模拟，这两种方法均基于经验力场来描述原子间的电势。两种技术均以其经典和量子力学版本进行了研究，以评估每种方法的准确性和局限性。特别要注意经典近似，准谐波近似无法捕获的动力学行为非谐的发生和有限大小效应。结果表明，在0小于或等于T小于或等于300 K的整个温度范围内，量子效应都是重要的。在低于熔融温度约2/3的温度下（即，聚乙烯为250 K），两种方法在给定的经验力场下，在经典和量子力学情况下均能产生一致的结果，但要避免有限的尺寸效应。高于300 K，非谐波效应变得非常明显。由于所需的仿真大小，在路径积分蒙特卡洛（PIMC）框架中对这些影响的综合处理使当前的计算可行性受到了限制。提供了在经典模拟，准谐波方法和全路径积分蒙特卡洛模拟之间进行选择的指南。 （C）1998美国物理研究所。 [参考：43]

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