Molecular non-equilibrium

Control in Non-Equilibrium-Molecular-Dynamics Simulations of the Shear Flow of Dense Liquids. 

Michel Mareschal, The Microscopic Approach to Complexity in Non-Equilibrium Molecular Simulations. Proceedings of the Euroconference held in Lyon, France, 15-19 July 1996, in Physica A (Amsterdam), 240 (1-2), Elsevier, Amsterdam, The Netherlands, 1997. 

The static and dynamic properties of polymer-layered silicate nanocomposites are discussed, in the context of polymers in confined spaces and polymer brushes. A wide range of experimental techniques as applied to these systems are reviewed, and the salient results from these are compared with a mean field thermodynamic model and non-equilibrium molecular dynamics simulations. 

In a somewhat similar paper, diffusion through a 2D porous solid modeled by a regular array of hard disks was evaluated [65] using non-equilibrium molecular dynamics. It was found that Pick s law is not obeyed in this system unless one takes different diffusion constants for different regions in the flow system. Other non-equilibrium molecular dynamics simulations of diffusion for gases within a membrane have been presented [66]. The membrane was modeled as a randomly... 

Molecular dynamics simulations entail integrating Newton s second law of motion for an ensemble of atoms in order to derive the thermodynamic and transport properties of the ensemble. The two most common approaches to predict thermal conductivities by means of molecular dynamics include the direct and the Green-Kubo methods. The direct method is a non-equilibrium molecular dynamics approach that simulates the experimental setup by imposing a temperature gradient across the simulation cell. The Green-Kubo method is an equilibrium molecular dynamics approach, in which the thermal conductivity is obtained from the heat current fluctuations by means of the fluctuation-dissipation theorem. Comparisons of both methods show that results obtained by either method are consistent with each other [55]. Studies have shown that molecular dynamics can predict the thermal conductivity of crystalline materials [24, 55-60], superlattices [10-12], silicon nanowires [7] and amorphous materials [61, 62]. Recently, non-equilibrium molecular dynamics was used to study the thermal conductivity of argon thin films, using a pair-wise Lennard-Jones interatomic potential [56]. 

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... 

D.J. Evans, W.G. Hoover, B.H. Failor, B. Moran, and A.J.C. Ladd (1983) Non-equilibrium molecular dynamics via Gauss s principle of least constraint. Phys. 

Non-equilibrium molecular dynamics Natural population analysis... 

However, for polymers with low degree of crystallization it was assessed that the melting point was depressed at high shear stresses (4). Shear Induced melting has been theoretically predicted from non-equilibrium molecular dynamic simulations (5,... 

Non-Equilibrium Molecular Dynamics Studies of Shock and Detonation Processes in Energetic Materials... 

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... 

Ladd A J C and Hoover W G 1983 Plastic-flow in close-packed crystals via non-equilibrium molecular-dynamics Phys. Rev. B 28 1756-62... 

The same effect in Zeolite-guest systems was demonstrated by Auerbach [26] by equilibrium molecular dynamics and non-equilibrium molecular dynamics after experimental work by Cormer [27]. The energy distributions obtained in Zeolite and Zeolite-Na are shown in Fig. 5.6A. At equilibrium, all the atoms in the system are at the same temperature. When Na-Y Zeolite is exposed to microwave energy, however, the effective steady-state temperature of Na atoms is substantially higher than that of the rest of the framework this is indicative of athermal energy distribution. The steady-state temperatures for binary methanol/benzene mixtures in... 

Non-equilibrium molecular dynamics Neutron spin-echo Legendre polynomial... 

Miiller-Plathe, F., Reith, D. Cause and effect reversed in non-equilibrium molecular dynamics an easy route to transport coefficients. Comput. Theor. Polymer Sci. 9, 203-209 (1999)... 

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. 

Some heat flows in connection with entropy production are associated with other thermodynamic variables. Typical single fluxes and forces are summarized above. It may be noted that steady fluxes are considered. Kinetic theory provides theoretical justification of some of these flux force relations (J = LX). Here, L is called phenomenological coefficient. But kinetic theory has limitation in the sense that first approximation to distribution function corresponds to local equilibrium hypothesis. It may be noted that non-equilibrium molecular dynamics (model and simulation) provides justification of these laws for a wide range. Nevertheless, justification has to be provided by experiments (Table 2.1). 

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. 

Non-equilibrium molecular dynamics simulations of transport processes can be done in two ways. 

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]. 

J.J. Erpenbeck, Non-Equilibrium Molecular Dynamics Calculations of the Shear Viscosity of Hard spheres in Non-polar Fluid behaviour, H.J.M. Hanley, (ed), North-Holland, Amsterdam, 1983. 

SEC was also used to study the transesterification reaction by following the rate of equilibration of PET samples with non-equilibrium molecular mass distributions. It was found that the cyclic trimer was more susceptable to alcoholysis than were linear oligomers. SEC was particularly useful in determining the cyclic trimer content in PET. 

W. T. Ashurst and W. G. Hoover, Argon shear viscosity via a Leonard-Jones potential with equilibrium and non-equilibrium molecular dynamics, Phys. Rev. Lett. 31, 206-207 (1973). 

B. L. Holian, W. W. Wood, and J. J. Erpenbeck, Self-diffusion of hard spheres and disks by non-equilibrium molecular dynamics (in preparation). 

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