Molecular-dynamics calculations of the velocity-autocorrelation function. Methods, hard-disk results
The velocity-autocorrelation function rho/sub D/(t) for hard disks is computed for ten values of the reduced volume, ranging from 30 to 1.4 times the close-packed volume (V/sub 0/) for systems of as few as 168 and as many as 5822 particles, by a Monte Carlo molecular-dynamics technique. For values of the time greater than roughly 20 mean-free times (t/sub 0/), the results are compared with the predictions of a version of the mode-coupling theory for rho/sub D/(t), modified to take into account the finite size of the system. Except at the highest densities, the data agree with the modified theory when one uses Enskog values for the transport coefficients in evaluating the theoretical rho/sub D/(t), provided the comparison is limited to times beyond a value s/sub i/t/sub 0/, with s/sub i/ dependent on the density. The value of s/sub i/ appears to increase from roughly 20 at the lowest densities to 40 at a volume of 2V/sub 0/. At volumes of 1.6, 1.5, and 1.4V/sub 0/, the theoretical rho/sub D/(t)'s are too large out to times as large as 320t/sub 0/, unless we use values of the transport coefficients rather larger than the Enskog values in evaluating the theoretical rho/sub D/(t). The velocity-autocorrelation-function results for t<20t/sub 0/ are presented as the difference relative to the Lorentz-Boltzmann-Enskog prediction, which has the exact slope at t = 0.
- Research Organization:
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545
- OSTI ID:
- 6789308
- Journal Information:
- Phys. Rev. A; (United States), Journal Name: Phys. Rev. A; (United States) Vol. 26:3; ISSN PLRAA
- Country of Publication:
- United States
- Language:
- English
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