The decay of pair correlations in quantum hard-sphere fluids.

A study of the asymptotic decay of the pair radial correlations in the bare quantum hard-sphere (QHS) fluid and in the quantum hard-sphere Yukawa (QHSY) fluid is presented. The conditions explored are far from quantum exchange and are contained within the region (0.1<or=rho(N) ()<or=0.8; 0.116 <or= lambda(B) ()<or= 0.9). The three types of pair radial correlations existing in path-integral quantum monatomic fluids (instantaneous, pair linear response and centroids) are analyzed by utilizing the complex poles methodology expounded by Evans et al. [J. Chem. Phys. 100, 591 (1994); Phys. Rev. E 59, 1435 (1999)] complemented with Ornstein-Zernike frameworks appropriate for quantum fluids. Given that there is no analytical theory of the quantum direct correlation functions, the present applications rely on the short-ranged methodology of asymptotics augmented with increasing ranges of the cutoff. The following main issues of interest are addressed: the influence of the sample size on the decay properties, the features of the pole patterns arising from the asymptotic calculations, and the effect of Yukawa attractions on the decay properties of systems composed of quantum hard spheres. The results show that the decays in the QHS fluid are of the exponentially damped oscillatory type, and hence no indication of Fisher-Widom lines has been found. On the other hand, in the QHSY fluid, both pure exponential (monotonic) and exponentially damped oscillatory decays may be obtained. Consequently, there is evidence that Fisher-Widom lines can be expected for the three pair radial correlations in the QHSY fluid.