Reverse Non-equilibrium Molecular Dynamics

Abstract

Abstract. We review non-equilibrium methods for calculating transport coefficients with emphasis on the reverse non-equilibrium molecular dynamics (RNEMD) method. It has fundamental and technical advantages over previous equilibrium and non-equilibrium techniques. For example, it applies the perturbation in a microcanonical way (no thermostat needed) and its raw data are well defined and robust gradients, rather than, fluxes which are often difficult to define and to calculate with sufficient accuracy. The method has so far been applied to the calculation of viscosities, thermal conductivities and Soret coefficients. Finally, the status and future potential of the RNEMD method are discussed.

A reverse nonequilibrium molecular dynamics method for calculating the mutual diffusion coefficient for binary fluids

“…We also note that even the strongest perturbation, t exch ¼14 ps, yields a reasonable D ArKr in spite of the huge concentration gradient. The mutual diffusion coefficients are thus independent of the concentration gradient or exchange period, indicating that there is an extended robust linear-response regime for the diffusion, which is in contrast to the application of RNEMD to viscosity calculations (Müller-Plathe and Bordat, 2004). The error increases with increasing exchange period, due to a lower signal-to-noise ratio for small perturbations-a well-known phenomenon in RNEMD calculations.…”

“…The mutual diffusion coefficient is independent from the magnitude of the concentration gradient in the mixture over a wide range. This indicates that the method is easily kept in the linearresponse regime, which makes it much more robust for mutual diffusion coefficients, than previously for thermal conductivities or shear viscosities, where a suitable exchange period had to be found by experimentation (Müller-Plathe and Bordat, 2004). The calculated mutual diffusion coefficient for 3000Ar/3000Kr is 2.637 0.19 10 -9 m 2 /s at 115.77 K and 101.3 kPa, which is in the range of liquids' diffusion coefficients (10 À 9 m 2 /s).…”

A molecular dynamics study of the thermal conductivity of nanoporous silica aerogel, obtained through negative pressure rupturing

“…Following this, the heat flux was imposed via reverse nonequilibrium MD (RNEMD) [23], by swapping energies once every 0.025 ps, while maintaining an average temperature of 300 K. This amount of swapping ensured a rapid convergence of the simulated temperature gradient, and produced a linear response within the simulation cell. Further details of RNEMD will be given in Section 2.3 below.…”

Correlation between thermal conductivity and bond length alternation in carbon nanotubes: A combined reverse nonequilibrium molecular dynamics—Crystal orbital analysis

“…56,57 Thus, it is not necessary to recapitulate its basic ingredients here. In the present context, we only want to mention that the determination of k in the RNEMD approach requires the formation of a linear temperature gradient.…”

“…For this purpose, we have supported RNEMD simulations 56,57 with the results of semiempirical crystal orbital (CO) calculations. The efficient electronic Hartree-Fock (HF) Hamiltonian adopted is of the intermediate neglect of differential overlap (INDO) type.…”