Argon velocity autocorrelation

Fig. 7.10 Velocity autocorrelation functions for liquid argon at densities of l.i% gem and0.863gcm...

It shows the clear link between the change of motion of the particle and its diffusion coefficient. In Fig. 50, the velocity autocorrelation function of liquid argon at 90 K (calculated by computer simulation) is shown [451], The velocity becomes effectively randomised within a time less than lps. Further comments on the velocity autocorrelation functions obtained by computer simulation are reserved until the next sub-section. Because the velocity autocorrelation function of molecular liquids is small for times of a picosecond or more, the diffusion coefficient defined in the limit above is effectively established and constant. Consequently, the diffusion equation becomes a reasonable description of molecular motion over times comparable with or greater than the time over which the velocity autocorrelation function had decayed effectively to zero. Under... 

Fig. 50. Velocity autocorrelation function for argon at 90 K. O, From the molecular dynamics calculation of Rahman [451] ——, from the Langevin approximation, exp — mDtfkuT D is taken as 2.72 X 10 9 m2 s"1.

Fig. 2. Error bounds for the cumulative frequency distribution of the spectral density for the velocity autocorrelation function using jU.0, /n2, and ja evaluated for a classical model of liquid argon.29...

The numerical calculations show that this theory can describe the velocity autocorrelation function (VACF) for liquid argon and rubidium [47] fairly well, and the agreements with the computer simulation studies [48, 49] were satisfactory. However, the numerical calculations needed the VACF as an input which was obtained from the respective computer simulation... 

We also adopt a similar description for the solvent. This type of model requires some comment, even when applied to the simple solvents such as dense liquid argon or other noble gases. Although the static structural properties of such fluids are represented quite well by taking into account only the strongly repulsive parts of the potential," the weak attractive forces do have noticeable effects on dynamic properties such as the velocity autocorrelation function.However, a model that includes only the repulsive forces is not unreasonable for a description of the solvent dynamics in dense liquids, and this expedient is adopted. We focus on general features that are not expected to be especially sensitive to this approximation. 

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