Friction coefficient of a Lennard-Jones fluid from the random force autocorrelation function determined as a memory function by molecular dynamics calculations

Journal Article · Sun Jan 01 04:00:00 EST 1989 · J. Stat. Phys.; (United States)

DOI:https://doi.org/10.1007/BF01023482· OSTI ID:6357005

Vogelsang, R; Hoheisel, C

A recent molecular dynamics (MD) study showed that the friction coefficient of a simple fluid is obtainable by the integral over the autocorrelation function (ACF) of the total force of a Brownian-type particle. The results indicated that mass ratio 50 less than or equal to M/m less than or equal to 200 of the massive and the light particle suffice to yield accurate friction coefficients. Complimentarily, they calculate the random force ACF of the light particle, which is the memory function force of the ACF of the velocity apart from a constant factor, for all the states of the Lennard-Jones system investigated previously. A detailed comparison is presented of the memory function, the total force ACF of the fluid particle, and the total force ACF of the massive particle. The MD results confirm quantitatively their theoretical predictions: (i) on a time scale corresponding to the dynamics of the massive particle the total force ACF of that particle approximates well the memory function, while there are slight differences between them on a short time scale, (ii) the total force ACF of the liquid particle deviates significantly from the memory function already after extremely short time and is thus completely useless for the determination of the friction coefficient, (iii) using the total force ACF of a heavy particle for the determination of the friction constant with mass ratio of M/m = 50 up to 200, the pseudo plateau value of the time integral is often not very noticeable, as the memory function is only approximated and the total force ACF of the massive particle has a negative part at medium times. In those cases the integration has to be extended to include the negative part.

• Research Organization: Theoretische Chemie, Bochum (West Germany)
• OSTI ID: 6357005
• Journal Information: J. Stat. Phys.; (United States), Journal Name: J. Stat. Phys.; (United States) Vol. 54:1-2; ISSN JSTPB
• Country of Publication: United States
• Language: English

Related Subjects

657002* -- Theoretical & Mathematical Physics-- Classical & Quantum Mechanics
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BROWNIAN MOVEMENT
COLLISIONS
CORRELATION FUNCTIONS
DIFFUSION
DYNAMICS
EQUATIONS
FLUIDS
FOURIER TRANSFORMATION
FRICTION FACTOR
FUNCTIONS
INTEGRAL EQUATIONS
INTEGRAL TRANSFORMATIONS
LAPLACE TRANSFORMATION
LENNARD-JONES POTENTIAL
LIQUIDS
MASS
MATHEMATICAL MODELS
MECHANICS
MOLECULAR MODELS
MOLECULE COLLISIONS
MOLECULE-MOLECULE COLLISIONS
MOLECULES
PARTICLES
POTENTIALS
SELF-DIFFUSION
STATISTICAL MECHANICS
THERMODYNAMICS
TRANSFORMATIONS
VOLTERRA INTEGRAL EQUATIONS