A simulation study of the quantum hard-sphere Yukawa fluid

Abstract

The quantum hard-sphere fluid with attractive Yukawa interactions is studied along several isochores, at low and medium densities, by varying the rest of the parameters that define its state points (the temperature, and the well-depth and inverse range of the attractive tail). Path integral Monte Carlo simulations are performed to fix the thermodynamics (energies and pressures) and the pair structures in r-space (instantaneous, linear response, and centroids). The k-space structure factors associated with these radial structures are determined via direct correlation functions defined by suitable Ornstein–Zernike equations. The results obtained allow one to assess quantitatively the reduction in the quantum features of the hard-sphere system due to the inclusion of attractive interactions. Besides, it is observed that under certain conditions the Yukawa interactions can lead to the formation of cavities in the system. For the sake of comparison, some complementary simulations of the bare quantum hard-sphere system have also been carried out, which have helped to resolve certain unclear features near a fluid–solid change of phase of this system. At the onset of increasing fluctuations in the Yukawa system one can observe, from the computation of k-space properties, the negligible role of the repulsive forces in this issue, and also the direct correlation function features associated with the attractions. In addition, the current quantum results give evidence of the decrease in both the critical temperature and the critical density of the Yukawa system, as compared with its classical counterpart.

Path integral Monte Carlo study of quantum-hard sphere solids

“…[26][27][30][31][32][42][43][44][45][46][47][48][49] Some of them are of interest to this work: the accurate equation of state for the fluid phase reported recently, 49 a preliminary study of the fluid-solid fcc transition for intermediate densities, 31,32 and also the computation of a number of properties of the fcc and bcc lattices. 30 With the better computational means of today this article is devoted to extending and completing the foregoing QHS results by studying the properties of the fcc, hcp, and bcc solid phases.…”

The decay of pair correlations in quantum hard-sphere fluids

“…In addition, other issues were addressed, such as the reconstruction of the input h(r) from the computed poles, or the possible existence of distinctive traits in the pole patterns as phase transitions were approached from the fluid branches. 40 Furthermore, it is also very interesting to remark that, although the bare QHS model has been successfully used to simulate the properties of fluid and solid helium, 41,42 the inclusion of Yukawa attractions outside the hard core makes this model more realistic ͑QHSY͒ and changes the bare QHS properties dramatically. 24,34 Given the absence of attractions and the stronger character of the quantum hardcore repulsion, as compared with its classical counterpart, this educated guess was expected to be sufficiently accurate to yield significant results.…”

“…It is worth remarking that the c(r) functions were assumed to be short-ranged in the sense c(r)ϭ0 for rуR Z , where the cutoffs were рR Z р2, as imposed by the simulation sample sizes employed (N s ϭ125 hard spheres͒. 40 In this regard, evidence of critical behavior has been found in the QHSY system for conditions ( N * , B *) under which QHS yields normal fluid phases. 27,34 Moreover, as a result of this assumption, all convergence problems present in the asymptotic calculations mentioned above were suppressed.…”

Semiclassical approach to model quantum fluids using the statistical associating fluid theory for systems with potentials of variable range

“…20 Other extensions and further analysis of this approach have been considered, 28, 29 including its connection to the path-integral description, 35 which is a robust approach to model quantum fluids, particularly in computer simulations. 10,[30][31][32][33][34] In this paper, we are interested in the modeling of thermodynamic properties of quantum fluids based on a WentzelKramers-Brillouin (WKB) extension of the statistical associating fluid theory (SAFT). 36,37 Over the years, SAFT has been a very powerful method to describe a wide range of systems, most of them of industrial interest, and different versions have been derived.…”