1305.3954 (Duane C. Wallace et al.)

Application of vibration-transit theory to distinct dynamic response for
a monatomic liquid    [PDF]

Duane C. Wallace, Eric D. Chisolm, Giulia De Lorenzi-Venneri

The purpose of this research is to apply vibration-transit (V-T) theory of monatomic liquid dynamics to the distinct part of the density autocorrelation function, Fd(q,t). A similar study has been reported for the self part [G. De Lorenzi-Venneri, E. D. Chisolm, and D. C. Wallace, Phys. Rev. E 78, 041205 (2008)], and it is necessary to study the self and distinct parts separately because their damping processes are not simply related. The theory is minimally calibrated, then tested, by means of Molecular Dynamics (MD) calculations for liquid Na at 395 K. Our formulation begins with the perfect vibrational system, which provides precise definitions of the liquid correlations, and provides the vibrational approximation Fdvib(q,t) at all q,t. Two independent liquid correlations are defined, motional and structural, and these are decorrelated sequentially, with a crossover time tc(q). A microscopic model is made for the "transit drift," the averaged transit motion that damps motional correlation on 0tc(q). The complete model explains the common MD property in both self and distinct decorrelation: simple exponential decay following a delay period, where the delay is tc(q), the time required for the random walk to emerge from the drift. The theory developed here provides an accurate account of Fd(q,t) for all q through the first peak in Sd(q), but a modification will be required at q where Sd(q) converges to zero. We note that V-T theory provides a unification of equilibrium and nonequilibrium statistical mechanics theories, unprecedented in liquid dynamics.

View original: http://arxiv.org/abs/1305.3954