Despite about forty years of investigations, the nature of the melting transition in two dimensions is not completely clear. In the framework of the most popular Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young (BKTHNY) theory, 2D systems melt through two continuous Berezinskii-Kosterlitz-Thouless (BKT) transitions with intermediate hexatic phase. The conventional first-order transition is also possible. On the other hand, recently on the basis of computer simulations the new melting scenario was proposed with continuous BKT type solid-hexatic transition and first order hexatic-liquid transition. However, in the simulations the hexatic phase is extremely narrow that makes its study difficult. In the present paper, we propose to apply the random pinning to investigate the hexatic phase in more detail. The results of molecular dynamics simulations of two dimensional system having core-softened potentials with narrow repulsive step which is similar to the soft disk system are outlined. The system has a small fraction of pinned particles giving quenched disorder. Random pinning widens the hexatic phase without changing the melting scenario and gives the possibility to study the behavior of the diffusivity and order parameters in the vicinity of the melting transition and inside the hexatic phase.
Structural behavior of a two length scale core-softened fluid in two dimensions
2D竞争系统显示了大量的各种固体和聚集模式，重入流体相，连续熔化的KTHNY理论预测，在某些情况下，水状异常。在本文中，我们采用朗之万动力学模拟的斜坡状核心软化流体，具有两个特征长度尺度和上述所有功能。通过分析该系统的流体相，Bordin和Barbosa [Phys. Rev. E 97，022604（2018）]报告了两个水状异常区域的存在。现在，我们重新审视这个问题，集中在低温制度和更大范围的密度寻找异常行为的起源，固相和重入熔化之间的关系。现在，不是两个，而是三个异常区域被观察到。这些异常区与非晶态固体向团簇流体的重入熔化有关。它们不仅受势中特征尺度之间的竞争支配，而且还受粒子构象变化引起的额外竞争支配。这种竞争从固相扩展到流体相，反映在构造水状异常上。我们的结果在两个长度尺度的竞争势的复杂行为的阴影一些光，并有助于阐明在这些系统中的大量的固相和存在一个以上的水状异常区域之间的关系。
Brownian dynamics study of driven partially pinned solid in the presence of square array of pinning centers: Enhanced pinning close to the melting transition
