Sesé Luis M
Departamento de Ciencias y Técnicas Fisicoquímicas, Facultad de Ciencias, Universidad Nacional de Educación a Distancia, Madrid, Spain.
J Phys Chem B. 2008 Aug 21;112(33):10241-54. doi: 10.1021/jp802542u. Epub 2008 Jul 24.
A computational study of gaseous helium-3 at T=5.23 K, for number densities rho N<0.0021 A(-3), analyzing the different pair and triplet structures in both the r and the k spaces, is presented. Structures in r space (i.e., instantaneous, total continuous linear response, and centroids) are determined via path-integral Monte Carlo simulations in the canonical ensemble by utilizing the Aziz-Slaman and the SAPT2 interatomic potentials. Additional results obtained with the application of two closures for triplets in r space, the Kirkwood superposition approximation and the Jackson-Feenberg convolution, are also reported. Besides, an analysis of the nonsuitability of quantum hard spheres for describing this system is included. The pair structures in k space are fixed via Ornstein-Zernike schemes appropriate for dealing with quantum diffraction effects in fluids. The effect on the quality of the computed isothermal compressibilities brought about by increasing the sample size in the simulations and by the subsequent application of a grand ensemble correction to the asymptotic behavior of the canonical pair radial correlation functions is also investigated. Furthermore, it is demonstrated analytically that the methods of classical statistical mechanics for dealing with the higher-order direct correlation functions remain fully valid for studying the higher-order correlations of path-integral centroids. By taking advantage of this result, the triplet structure factors for the centroid (also for the instantaneous) correlations are computed by following a number of distinct closures and methods that involve triplet direct correlation functions. The latter computations are intended to explore an alternative scheme to the very expensive fixing of triplet structure factors through direct path integral simulations, an alternative which is expected to yield the main features of these triplet quantities for this gas. Comparison with experiment is made wherever possible, and the results presented allow one to explain the substantial structural features existing in gaseous helium-3.
本文给出了在温度T = 5.23 K、数密度ρN < 0.0021 Å⁻³条件下气态氦-3的计算研究，分析了r空间和k空间中的不同对结构和三重态结构。通过在正则系综中利用阿齐兹 - 斯拉曼和SAPT2原子间势进行路径积分蒙特卡罗模拟，确定了r空间中的结构（即瞬时、总连续线性响应和质心结构）。还报告了应用r空间中三重态的两种封闭近似（柯克伍德叠加近似和杰克逊 - 芬伯格卷积）得到的其他结果。此外，还包括对量子硬球不适用于描述该系统的分析。k空间中的对结构通过适用于处理流体中量子衍射效应的奥恩斯坦 - 泽尼克方案确定。还研究了模拟中增加样本大小以及随后对正则对径向关联函数的渐近行为应用巨正则系综校正对计算的等温压缩率质量的影响。此外，通过分析证明，处理高阶直接关联函数的经典统计力学方法对于研究路径积分质心的高阶关联仍然完全有效。利用这一结果，通过遵循一些涉及三重态直接关联函数的不同封闭近似和方法，计算了质心（也包括瞬时）关联的三重态结构因子。后一种计算旨在探索一种替代方案，以替代通过直接路径积分模拟非常昂贵地确定三重态结构因子，预计该替代方案能够给出这种气体这些三重态量的主要特征。尽可能与实验进行了比较，所呈现的结果有助于解释气态氦-3中存在的大量结构特征。
