Title: COLLECTIVE DYNAMICS IN SINGLE-PARTICLE MOTION FOR PURE FLUIDS
Author(s): T.M.Bryk (Department of Chemistry, University of Houston, Houston, TX 77204, USA; Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine), I.M.Mryglod (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine), A.D.Trokhymchuk (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine; Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602, USA)

Single-particle time correlation function $F_s (k,t)$ of pure fluids is studied within the generalized mode approach. Analytical expression for self-intermediate scattering function, which contains oscillating terms, is obtained for three-variable basis set of single-particle dynamic variables. The meaning of oscillating contributions is discussed, and it is shown, that in low-density fluids the oscillating contributions do not appear. Our approach, developed within the five-variable scheme, is used for the analysis of MD-derived single-particle time correlation function of Lennard-Jones fluid at two densities. It is shown, that the proposed scheme allows us to reproduce perfectly the function $F_s (k,t)$ at the whole range of wavenumbers $k$ studied. The generalized self-diffusion coefficient as a function of $k$ is also calculated.

Key words: single-particle dynamics, Lennard-Jones fluid, velocity autocorrelation function, diffusion
PACS: 05.20.Jj, 61.20.Lc