Localization in a Lennard-Jones fluid: The path-integral approach

The equilibrium properties of a light particle (LP) in a dense fluid are investigated analytically and numerically. It is assumed that the fluid molecules interact via a Lennard-Jones 6,12 potential and that the LP is a rigid sphere. The path-integral RISM model of the LP developed by Chandler et al. is employed, extended to include the smooth intermolecular interaction, to investigate the quantum dispersion of the position of the LP and the LP-fluid radial distribution function, g(r). It is found that important changes in g(r) occur in a region of the liquid-vapor critical point of the fluid that are qualitatively similar to the properties of the ‘‘self-trapped’’ states that arise in the earlier density functional theories. It is demonstrated that the thermodynamic pressure and compressibility exert a competing influence on g(r), and evidence is presented that the usual understanding of localization in fluids has to be extended.