This paper reports on the molecular dynamics simulations of classical two-dimensional (2D) electric dipole systems. The properties of 2D systems with bare (nonscreened) and screened dipole-dipole interactions have been investigated. Based on the polygon construction method, we present simulation results on the phase transition, and we locate the melting and freezing points of 2D dipole systems in terms of a polygon disorder parameter, with the polygon disorder parameter being the sum of nontriangular polygon order parameters. It was found that the phase transition of the system occurs when the polygon disorder parameter has a value 0.165. This result was cross-checked by using both local and overall orientational order parameters. We also identified that the value of the average local orientational order parameter at the phase transition point is 0.67. These results are valid for the ordinary (bare) dipole-dipole interaction as well as the screened dipole-dipole interaction, and they are expected to be general for other 2D systems with repulsive pair interaction. We observed that both melting and freezing points shift to lower values of temperature due to screening. In the liquid state, the radial distribution function and polygon construction method show the loss of order in a structure as screening becomes more severe. Furthermore, the impact of screening on the system's collective excitation spectra and diffusive characteristics at liquid and solid states has been studied. Results show the decrease in the values of both longitudinal and transverse sound speeds and the emergence of anomalous superdiffusive motion in the liquid state due to screening.

中文翻译：

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筛选偶合介质中二维偶极子系统的融化，冻结和动力学

本文报道了经典二维（2D）电偶极子系统的分子动力学模拟。研究了具有裸露（非屏蔽）和屏蔽偶极-偶极相互作用的二维系统的特性。基于多边形构造方法，我们给出了相变的仿真结果，并根据多边形无序参数确定了二维偶极子系统的熔点和凝固点，多边形无序参数是非三角形多边形阶次参数的总和。已经发现，当多边形无序参数的值为0.165时，会发生系统的相变。通过使用局部和整体定向顺序参数对此结果进行了交叉检查。我们还确定，在相变点处的平均局部取向顺序参数的值为0.67。这些结果对于普通（裸）偶极子-偶极子相互作用以及筛选的偶极子-偶极子相互作用都是有效的，并且预期它们对于具有排斥对相互作用的其他2D系统是通用的。我们观察到，由于筛选，熔点和凝固点均移至较低的温度值。在液体状态下，随着筛选变得更加严格，径向分布函数和多边形构造方法显示出结构中的有序损失。此外，还研究了屏蔽对系统集体激发光谱和液态​​和固态扩散特性的影响。