The phase diagram of the prototypical two-dimensional Lennard-Jones (LJ) system, while extensively investigated, is still debated. In particular, there are controversial results in the literature with regard to the existence of the hexatic phase and the melting scenario. Here we study the phase behavior of two-dimensional range-limited LJ particles via large-scale numerical simulations. We demonstrate that at a high temperature, when the attraction in the potential plays a minor role, melting occurs via a continuous solid-hexatic transition followed by a first-order hexatic-fluid transition. The hexatic phase occurs in a density range that vanishes as the temperature decreases so that at low-temperature melting occurs via a first-order liquid-solid transition. The temperature where the hexatic phase disappears is well above the liquid-gas critical temperature. The evolution of the density of topological defects confirms this scenario.

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Lennard-Jones粒子在二维中的相行为

典型的二维Lennard-Jones（LJ）系统的相图虽然经过了广泛研究，但仍在争论中。特别地，在文献中关于六相相的存在和熔化情况存在有争议的结果。在这里，我们通过大规模数值模拟研究二维范围受限的LJ粒子的相行为。我们证明，在高温下，当电势中的吸引力起次要作用时，熔融会通过连续的固-六相转变和随后的一阶六-相转变而发生。六方相的密度范围随温度降低而消失，因此在低温下会通过一级液固转变发生熔化。六方相消失的温度远高于液化气临界温度。拓扑缺陷密度的演变证实了这种情况。