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arXiv 0912.2280cond-mat.stat-mech
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限制吉布斯系综模拟的流体相共存和临界行为

Fluid phase coexistence and critical behaviour from simulations in the restricted Gibbs ensemble

Douglas J. Ashton, Nigel B. Wilding, Peter Sollich

摘要:

对称限制吉布斯系综(英语:symmetric restricted Gibbs ensemble,RGE)是吉布斯系综的一个版本,其中粒子在两个固定相等体积的盒子之间交换。它最近变得突出,因为-当与专门的算法相结合时-它提供了在高度尺寸不对称的二元混合物中的近共存密度波动的研究。然而,迄今为止,从RGE密度波动中提取临界点和共存曲线参数的准确估计的详细框架一直缺乏。在这里,我们解决这个问题,利用RGE密度波动和巨正则系综之间的确切联系。在亚临界区域,我们提出并测试了一种简单的方法来获得共存密度的准确估计。在临界区域中,我们确定了一个观察,作为一个有限的系统尺寸估计的临界点参数,并提出了一个有限尺寸标度理论,允许外推到热力学极限。

英文摘要:

The symmetrical restricted Gibbs ensemble (RGE) is a version of the Gibbs ensemble in which particles are exchanged between two boxes of fixed equal volumes. It has recently come to prominence because -- when combined with specialized algorithms -- it provides for the study of near-coexistence density fluctuations in highly size-asymmetric binary mixtures. Hitherto, however, a detailed framework for extracting accurate estimates of critical point and coexistence curve parameters from RGE density fluctuations has been lacking. Here we address this problem by exploiting an exact link between the RGE density fluctuations and those of the grand canonical ensemble. In the sub-critical region we propose and test a simple method for obtaining accurate estimates of coexistence densities. In the critical region we identify an observable that serves as a finite system size estimator for the critical point parameters, and present a finite-size scaling theory that allows extrapolation to the thermodynamic limit.

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