Non-equilibrium Molecular Dynamics NEMD

Non-equilibrium Molecular Dynamics, NEMD, is the application of molecular dynamics simulation to investigate the response of liquids to the effects of 

Another topic of recurring interest associated with the simulation of shear flow in atomic liquids is the shear-rate dependence of the viscosity, pressure and other thermodynamic quantities. Marcelli et al. performed homogeneous shear flow NEMD on a fluid interacting with two-body, (p2, and three-body, 3, terms in the interaction potential. The three-body potential term was 

New ways of applying non-equilibrimn states in molecular dynamics continue to be invented. Arya et al. devised a novel NEMD method for extracting the shear viscosity. The method follows the decay of a Gaussian velocity profile in a simulation cell, u (y, 0) = uq exp(—Z oy ). An analytic solution of the Navier-Stokes equation leads to a decay of the central or peak velocity, i/p, according to 

New developments in the theory of non-equilibrium fluids continues to bring out new and fascinating formulae. Searles and Evans developed further a fluctuation theorem which gives the probabiUty of observing second law violating dynamical fluctuations in finite sized non-equilibrium systems. The key formula is 

Another aspect of non-equilibrium relaxation was considered by Barrat and 

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Non-Equilibrium Molecular Dynamics (NEMD) Shockwave Simulations... 

The earliest efforts to develop non-equilibrium molecular dynamics (NEMD) methods used special boundary conditions and/or external fields to induce non-equilibrium behavior in the system. Important contributions to this development include those of Lees and Edwards [72], Gosling et al. [73], Hoover and Ashurst [74] and Ciccotti and Jacucci... 

Kinetic theory, non-equilibrium statistical mechanics and non-equilibrium molecular dynamics (NEMD) have proved to be useful in estimating both straight and cross-coefficients such as thermal conductivity, viscosity and electrical conductivity. In a typical case, cross-coefficient in case of electro-osmosis has also been estimated by NEMD. Experimental data on thermo-electric power has been analysed in terms of free electron gas theory and non-equilibrium thermodynamic theory [9]. It is found that phenomenological coefficients are temperature dependent. Free electron gas theory has been used for estimating the coefficients in homogeneous conductors and thermo-couples. 

Subsequent efforts have been made to extend the domain of validity of nonequilibrium thermodynamics by incorporating newer concepts of extended irreversible thermodynamics (BIT) and non-equilibrium molecular dynamics (NEMD). However, these are limited applicability as discussed in Appendices I-III of Part One. 

In non-equilibrium molecular dynamics (NEMD), a driving force is introduced which maintains the system out of equilibrium at steady state, or else a perturbation is introduced and the system studied as it relaxes towards equilibrium. Our simulations are of the latter type. Generation of the initial cells... 

The second attempt used non-equilibrium molecular dynamics (NEMD) [64]. Here, an artificial force F acts on the penetrants and the diffiiaon coefiicient is calculated assuming a linear response... 

A few theoretical and computational studies have already addressed in some detail the problem of viscosity in ILs.[136] However, a complete microscopic theory of viscosity is currently not available. It is a challenging task to accurately compute the viscosity of a complex system by means of simulation methods. For a system with high viscosity, it is extremely difficult to reach the hydrodynamic limit (zero wave number) where the experimental data is observed. This is because, in order to reach this limit, a very large simulation box is required. Traditional simulation methods normally used for shear viscosity of fluids fall into two categories (a) the evaluation of the transverse-current autocorrelation function (TCAC) through equilibrium molecular dynamics (HMD) trajectories and (b) non-equilibrium molecular dynamics (NEMD) simulations that impose a periodic perturbation. [137] In recent work, Hess[138] compared most of the above methods by performing simulations of Lermard-Jones and water system. They concluded that the NEMD method using a periodic shear perturbation can be the best option. 

Abstract Non-equilibrium thermodynamics offers a better and more precise way to describe transport of heat and mass over membranes than the simple Pick and Fourier models. In this work, we derive the equations for single component transport (of n-butane) across a zeolite membrane. We use non-equilibrium molecular dynamics (NEMD) data to show how transport phenomena are related. Significant differences are discussed between this method, and methods invoking Pick s and Fourier s laws. 

R0sjorde et al studied the phase transition in a pure fluid using non-equilibrium molecular dynamics simulations (NEMD). The NEMD method solves Newton s equations of motion for several thousand particles in an imaginary box see Hafskjold for a review. The particles interacted with a Lennard-Jones-type pair... 

The derivation of Dt from coherent QENS is similar to a computation of Dt from the fluctuations in an equilibrium density distribution. This was accomplished by Tepper and co-workers for Ar in AIPO4-5 [6]. Using the Green-Kubo formahsm, they were able to extract this non-equilibrium quantity from just one equihbrium simulation. Moreover, the calculations being performed in reciprocal space, the variation of the diffusivity upon the wave vector was used to check when the system was in the linear regime [6]. The first application of non-equihbrium molecular dynamics (NEMD) to zeolites was performed by Maginn et al. on methane in sihcalite [7]. Standard equi-libriiun MD techniques were later used by Sholl and co-workers to determine the concentration dependence of diffusivities [8]. 

Computation of shear viscosity of hard spheres has been attempted using NEMD [11], Modified non-equilibrium molecular dynamics methods have also been developed for study of fluid flows with energy conservation [12], NEMD simulations have also been recently performed to compare and contrast the Poiseuille and Electro-osmotic flow situations. Viscosity profiles obtained from the two types of flows are found to be in good mutual agreement at all locations. The simulation results show that both type of flows conform to continuum transport theories except in the first monolayer of the fluid at the pore wall. The simulations further confirm the existence of enhanced transport rates in the first layer of the fluid in both the cases [13, 14]. 

Normally, MD is performed at constant volume and constant total energy, yielding a microcanonical ensemble. For various reasons this is not very convenient and many approaches have appeared in the literature to yield a type of dynamics in which temperature and pressure are independent variables rather than derived properties. When MD is performed in non-equilibrium situations (NEMD non-equilibrium molecular dynamics) in order to study irreversible processes and transport properties, the... 

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