Abstract
The relaxation from a non-equilibrium state to the equilibrium depends on the methodologies and initial conditions. To investigate the microscopic mechanisms of equilibration systematically, we focus on the non-equilibrium response during the equilibration process induced by a disturbance of the homogeneous expansion of the simple hard disk systems. Large scale simulations by event-driven molecular dynamics revealed that an anomalous slow equilibration toward the liquid states emerges when starting from the co-existence phase. The origin of the slow decay mechanism is investigated using the probability distribution of local density and orientational order parameter.Their inhomogeneities seem to cause the anomalous slow equilibration.
Highlights
Introduction and Newtonian EventChain MC [12]
Any arbitrary states in the many-body systems will relax toward the statistical equilibrium state if you perform standard molecular simulations, which are the molecular dynamics using Newton’s equation of motion and sampling using Markov chain Monte Carlo [1]
We focus on the non-equilibrium response around the Alder transition in the large-scale 2D hard disk systems and investigate the non-equilibrium response to calculate each physical property against disturbance, i.e., homogeneous expansion as the simplest case, to the system
Summary
(In the recent large scale hard disk simulation [8, 9], the phase changes from the liquid (ν < 0.700), co-existence (0.700 < ν < 0.716), hexatic (0.716 < ν < 0.720) and solid (crystal) (ν > 0.720), respectively.) As the initial states, the systems for each packing fraction above the transition ν = 0.700 ∼ 0.722 are carefully prepared after long-time equilibration by efficient ECMC [7] up to 1013 collisions. We investigate the non-equilibrium response during equilibration focusing on the relaxation times of various physical properties O(t), such as pressure P∗, local and global orientational order parameters Φ6L and ΦG6 , and the number of nearest neighbor disks Ni. Since O(t) changes from O(0) to O(∞) = Oeq in which Oeq is the equilibrium values at the target packing fraction (i.e., νtarget = 0.698), we defined a function of relaxation F (t) = (O(t) −. We carefully optimize the filter parameters for smoothing not to affect the central claim of the results
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