Transport properties of bulk water at 243–550 K: a Comparative molecular dynamics simulation study using SPC/E,TIP4P,and TIP4P/2005 water models

ABSTRACT

Molecular dynamics simulations of various water models – SPC/E (extended simple point charge), TIP4P (transferable intermolecular potential 4 points), and TIP4P/2005 – have been carried out in the canonical (NVT fixed) ensemble over the range of temperatures 243–550?K with Ewald summation. The transport properties (self-diffusion coefficients D, viscosities η, and thermal conductivities λ) of SPC/E, TIP4P, and TIP4P/2005 water were evaluated at 243–550?K and compared with experimental data. The temperature dependence of transport properties of SPC/E, TIP4P and TIP4P/2005 water was discussed to determine how reliable the models are over this temperature range.     

Periodic orbit expansions for the Lorentz gas

We apply the periodic orbit expansion to the calculation of transport, thermodynamic, and chaotic properties of the finite-horizon triangular Lorentz gas. We show numerically that the inverse of the normalized Lyapunov number is a good estimate of the probability of an individual periodic orbit. We investigate the convergence of the periodic orbit expansion and compare it with the convergence of the cycle expansions obtained from the Ruelle dynamical -function. For this system with severe pruning we find that applying standard convergence acceleration schemes to the periodic orbit expansion is superior to the dynamical -function approach. The averages obtained from the periodic orbit expansion are within 8% of the values obtained from direct numerical time and ensemble averaging. None of the periodic orbit expansions used here is computationally competitive with the standard simulation approaches for calculating averages. However, we believe that these expansion methods are of fundamental importance, because they give a direct route to the phase space distribution function.     

Asymptotic time behavior of correlation functions. II. Kinetic and potential terms

On the basis of the mode-coupling theory we obtain the long-time behavior t ^–d/2 for the kinetic, potential, and cross-terms in the Green-Kubo integrands, expressed completely in terms of transport coefficients and thermodynamic quantities. All two-mode amplitudes are explicitly evaluated in terms of measurable quantities such as specific heats, thermal expansion coefficients, etc.     

Asymptotic time behavior of correlation functions. III. Local equilibrium and mode-coupling theory

The decay to equilibrium is discussed from a general point of view based on the assumed rapid approach to local equilibrium for well-chosen initial states. The assumption is applied to the problem of time correlation functions and it is shown that the mode-coupling formula describes the asymptotics of the so-called projected wavenumber-dependent correlation functions. The local equilibrium assumption thus provides a general basis for thet ^–3/2 behavior of correlation functions derived in previous papers in this series, as well as for the infinite series of correction termst ^–(2–Pn (n 2), withPn=2^–n, and for the corresponding series of corrections of orderk ^3–Pn (n1) to Navier-Stokes hydrodynamics.     

Influence of the interatomic potential on thermotransport in binary liquid alloys: case study on NiAl

Equilibrium molecular dynamics simulation in conjunction with the Green-Kubo formalism is employed to study the transport properties of a model Ni₅₀Al₅₀ melt with the embedded-atom method potential developed in [G.P. Purja Pun, Y. Mishin, Phil. Mag., 2009, 89, 3245]. The principal objective of the work is to quantitatively characterise and analyse thermotransport in the system, i.e. diffusion driven by a temperature gradient. In addition, direct phenomenological coefficients for mass and thermal transport are also evaluated and analysed in the process. Furthermore, the results obtained are compared with previously published data for a different model of Ni₅₀Al₅₀ melt with an alternative embedded-atom method potential for the alloy as well as with experiment where possible. It is found that both potentials are able to consistently predict both direct transport coefficients over a wide temperature range. However, these two potentials are found to be inconsistent in characterising the cross-coupled heat and mass transport, predicting even different directions (sign) of the heat of thermotransport. The origin of this difference is discussed in the paper in detail.     

The First Principle Calculation of Green—Kubo Formula with the Two—Time Ensemble Technique

For weak-coupling electronic plasmas in the presence of small fluctuations,we calculate Green-Kuboformula for transport coefficients employing the ab initio theory,i.e.,the two-time ensemble technique.The microscopic interpretations of Onsager‘s hypothesis on fluctuations are presented in the framework.     

Spatial‐Decomposition Analysis of Electrical Conductivity

Spatial decomposition is conducted for the electrical conductivity. The contribution per ion pair at a certain distance is identified in terms of a two‐body velocity time correlation function and is integrated over the whole distance of the ion pair to provide the cross‐correlation term of the conductivity. The spatial‐decomposition formula is an exact expression at any concentrations of ions and incorporates physically appealing pictures in the space domain into the theory of time correlation functions. Illustrative analyses are presented for 1m NaCl aqueous solution and the [C₄mim][NTf₂] ionic liquid. The contrast between the two systems is discussed for the time and spatial ranges of correlations, and it is shown that the ion‐pair contribution to the conductivity for the [C₄mim][NTf₂] system is not localized and extends beyond the first coordination shell of the cation‐anion pair.     

水导热系数的分子动力学模拟

本文选用平衡分子动力学模拟方法,应用不同的势能模型对强极性分子水的导热系数进行了模拟计算.结果表明,用分子动力学模拟方法计算水的导热系数时,模拟结果对模型的选取极为敏感.在目前应用较为广泛的几种模型中以TIP4P模型较为适用,所得的导热系数与实验值较为接近.     

Long-time tails of the green-kubo integrands for a binary mixture

The long-time tails for the mutual diffusion coefficient, the thermal diffusivity, the thermal conductivity, and the shear and longitudinal viscosities (from which the tail of the bulk viscosity can be calculated) of a nonreactive binary mixture are calculated from mode-coupling theory, and compared with a prior calculation by Pomeau. Three different choices of the thermal forces and currents are considered, with the results found to take their simplest form in the case of the de Groot double-primed set. The decompositions into the kinetic, potential, and cross terms are given.     

Interface motion in models with stochastic dynamics

We derive the phenomenological dynamics of interfaces from stochastic microscopic models. The main emphasis is on models with a nonconserved order parameter. A slowly varying interface has then a local normal velocity proportional to the local mean curvature. We study bulk models and effective interface models and obtain Green-Kubo-like expressions for the mobility. Also discussed are interface motion in the case of a conserved order parameter, pure surface diffusion, and interface fluctuations. For the two-dimensional Ising model at zero temperature, motion by mean curvature is established rigorously.