Search

Expressions for second and fourth sum rules of velocity autocorrelation function have been derived for fluid confined to a rectangular nanotube. Expressions obtained for these sum rules involve density profiles which vary with distance from walls of the tube. These sum rules, incorporating the effect of static changes made due to confinement, and the model which involves dynamical effect have been coupled to study the self-diffusion coefficient. By considering model density profiles, it is found that the self-diffusion coefficient in a direction perpendicular to the wall behaves differently from that in a direction parallel to the wall. The perpendicular diffusion coefficient is found to be more strongly dependent on the width of the tube than the parallel diffusion. It is found that dynamical effects are more in the region that is near to the confining wall than the static effects which track density profile. [ABSTRACT FROM PUBLISHER]

Abstract: Self-diffusion coefficient and velocity auto correlation function of fluid interacting via the Gaussian core potential have been studied using Mori–Zwanzig memory function formalism. Two and three body contributions to second and fourth frequency sum rules of velocity auto correlation function have been calculated. These sum rules and an ansatz for the memory function have been used to study the time evolution of velocity auto correlation function for different densities and temperatures. Results obtained are compared with the available molecular dynamics simulation results and are found to be in good agreement. Contribution due to three body correlations is found to play a significant role in anomalous behaviour of self-diffusion coefficient and velocity auto correlation function. [Copyright &y& Elsevier]

The dynamics of fluid contained in a nano-cube has been studied by proposing theoretical model which is based on the microscopic consideration. The confinement affecting the movement at atomic level has been used to study the self-diffusion through Green Kubo relation. It is found that close to the walls, the dynamics of fluid slows down to an extent that it affects the flow of fluid even in the middle of the nanocube. Results are contrasted with the results obtained from similar considerations for fluid confined in rectangular nanotube. It is found that tendency of freezing near the wall is more in case of nanocube than in the rectangular nanotube. An empirical relation has also been proposed to explain the behaviour of wall mediated self-diffusion as a function of distance in either direction. [ABSTRACT FROM AUTHOR]

A new form of Memory Function (MF) appearing in the Mori's formalism has been derived using plausible approximations. In addition to the fact that present form of MF satisfies sum-rules upto sixth order, it has special characteristic of presence of one more adjustable parameter. It is also found that the present form of MF behaves as sech ν ( bt ) under suitable conditions. The utility of the present MF is exemplified by studying time evolution of velocity auto correlation function and transport coefficients of Lennard-Jones fluids. [ABSTRACT FROM AUTHOR]