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J Chem Phys. 2013 Feb 21;138(7):074901. doi: 10.1063/1.4791635.
Phase separation of the ultrasoft restricted primitive model (URPM) with gaussian charges is re-investigated in the random phase approximation (RPA)--the "Level A" approximation discussed by Nikoubashman, Hansen, and Kahl [J. Chem. Phys. 137, 094905 (2012)]. We find that the RPA predicts a region of low temperature vapour-liquid coexistence, with a critical density much lower than that observed in either simulations or more refined approximations (we also remark that the RPA critical point for a related model with Bessel charges can be solved analytically). This observation suggests that the hierarchy of approximations introduced by Nikoubashman et al. should be analogous to those introduced by Fisher and Levin for the restricted primitive model [Phys. Rev. Lett. 71, 3826 (1993)], which makes the inability of these approximations to capture the observed URPM phase behaviour even more worthy of investigation.
我们重新研究了高斯荷超软限制原胞模型（URPM）的液-气相分离，这是 Nikoubashman、Hansen 和 Kahl [J. Chem. Phys. 137, 094905 (2012)] 讨论的“Level A”近似。我们发现 RPA 预测了一个低温汽-液共存区域，其临界密度远低于模拟或更精细的近似值（我们还注意到，具有贝塞尔荷的相关模型的 RPA 临界点可以解析求解）。这一观察结果表明，Nikoubashman 等人引入的近似层次应类似于 Fisher 和 Levin 为限制原胞模型引入的层次 [Phys. Rev. Lett. 71, 3826 (1993)]，这使得这些近似无法捕捉到观察到的 URPM 相行为更值得研究。
