Molecular dynamics test of the Brownian description of Na/sup +/ motion in water

Journal Article · Sun Dec 01 04:00:00 EST 1985 · J. Chem. Phys.; (United States)

OSTI ID:6405002

Wilson, M A; Pohorille, A; Pratt, L R

The autocorrelation function of the velocity of an infinitely dilute Na/sup +/ ion in aqueous solution, and the autocorrelation function of the force exerted on a stationary Na/sup +/ under the same conditions are evaluated by molecular dynamics calculations. The results are used to test the accuracy of Brownian motion assumptions which are basic to hydrodynamic models of ion dynamics in solution. The self-diffusion coefficient of the Na/sup +/ ion predicted by Brownian motion theory is (0.65 +- 0.1) x 10/sup -5/cm/sup 2//s. This value is about 60% greater than the one obtained for the proper dynamics of the finite mass ion, (0.4 +- 0.1) x 10/sup -5/cm/sup 2//s. The numerically correct velocity autocorrelation function is nonexponential, and the autocorrelation of the force on the stationary ion does not decay faster than the ion velocity autocorrelation function. Motivated by previous hydrodynamic modeling of friction kernels, we examine the approximation in which the memory function for the velocity autocorrelation function is identified with the autocorrelation function of the force on the stationary ion. The overall agreement between this approximation for the velocity autocorrelation function and the numerically correct answer is quite good.

• Research Organization: Department of Chemistry, University of California, Berkeley, California 94720
• OSTI ID: 6405002
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 83:11; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
AQUEOUS SOLUTIONS
BROWNIAN MOVEMENT
CHARGED PARTICLES
DIFFUSION
DISPERSIONS
HYDROGEN COMPOUNDS
INTERFACES
IONS
MIXTURES
OXYGEN COMPOUNDS
SODIUM IONS
SOLUTIONS
WATER