Title: Structural relaxation in pure liquids: Analysis of wavenumber dependence within the approach of generalized collective modes
Author(s):

	T.Bryk (Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii St., 79011 Lviv, Ukraine; Institute of Applied Mathematics and Fundamental Sciences Lviv Polytechnic National University, 12 Bandery Str., 79013 Lviv, Ukraine ) ,
	I.Mryglod (Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii St., 79011 Lviv, Ukraine; Institute of Applied Mathematics and Fundamental Sciences Lviv Polytechnic National University, 12 Bandery Str., 79013 Lviv, Ukraine ) ,

Wavenumber dependence of structural relaxation in liquids is studied by the method of generalized collective modes (GCM). A new perturbation approach within the GCM method is proposed and applied in the long-wavelenth limit in order to obtain analytical expressions for the wavenumber-dependent structural relaxation and sound dispersion within a simplified three-variable dynamical model. Analytical results are compared with numerical study of generalized modes within a more general five-variable dynamical model, which accounts for thermal processes in liquids. Numerical results are presented for four thermodynamic points of Lennard-Jones fluid at the reduced temperature T^*=1.71. We discuss the features of non-hydrodynamic process of structural relaxation in different regions of wavenumbers.

Key words: generalized hydrodynamics, structural relaxation, dynamical models, sound excitations, positive dispersion
PACS: {05.20.Jj, 61.20.Lc, 62.60.+v}