Computer Physics Reports最新文献

This report is an attempt to reconcile the macroscopic and microscopic views of rheology. Some essential relationships in non-equilibrium molecular dynamics, MD, are derived. These relate the stress response of a fluid to an arbitrary strain rate in terms of time correlation functions linking the stress in an equilibrium ensemble and the stress in the perturbed ensemble. It is shown how these expressions can be made use of in applied statistical mechanics via MD. There is a chapter on algorithmic implementation of these equations. An overview of the behaviour of simple fluids under non-Newtonian shear rates is given, summarising the work to date.

Recent extensions of this approach to multi-component macromolecular suspensions is given. The Strict Langevin equation representing the motion of the macromolecules is combined with the Lees-Edwards shear flow algorithm of MD. This leads to Brownian and diffusive dynamics schemes that reproduce the essential rheology of these systems.

The determination of transport coefficients of liquids by molecular dynamics methods is described. Both non-equilibrium (NEMD) and equilibrium molecular dynamics (MD) are considered. However, while the MD is exhaustively treated, NEMD methods are reported only briefly. For the latter, we are only concerned with the so-called subtraction technique. One- and two-component systems are considered modelled by Lennard-Jones 1-centre pair potentials. In some cases also results virtually corresponding to the triple point of argo. However, for comparison with experimental data, we consider further thermodynamic states. For the two-component system, we frequently treat the Ar-Kr system at a liquid state to allow comparison with experimental data. In detail are discussed the time correlation functions for: the self-diffusion coefficient, the mutual diffusion coefficient, the bulk and shear viscosity, the thermal conductivity and the thermal diffusion coefficient (Soret/Dufour effect). The detailed molecular formulation of the various currents, e.g. the pressure tensor elements, are given. The partial contributions of these to the total correlation functions are separately analysed. Technical details of the computations are presented, and the accuracy of the calculated coefficients is thoroughly estimated. Relations to scattering correlation functions are outlined and some results for wave-vector dependent tranport coefficients are presented for comparison. We conclude the article with a limited comparison of computed and measured data for Ar and Ar-Kr.

This article reviews various methods for the Monte Carlo simulation of models for long flexible polymer chains, namely self-avoiding random walks at various lattices. This problem belongs to the classical applications of Monte Carlo methods since more than thirty years, and numerous techniques have been devised. Neverthless, there are still many open questions, relating to the validity of the algorithms in principle, as well as to the accuracy of the results that can be obtained in practice. This review presents a brief introduction to these problems, discusses the basic ideas on which the various algorithms are based as well as their limitations, and describes a few typical physical applications. Most emphasis is on the simulation of single, isolated chains representing macromolecules in dilute solution, but the simulation of many-chain systems is also dealt with briefly. An outlook on related problems (simulation of off-lattice chains, branched instead of linear polymers, etc.) is also given, as well as discussion of prospects for future work.

There has been a renewed interest in the time-dependent quantum mechanical approach to reactive scattering in the last few years. Many of the bottlenecks in numerically solving the time-dependent Schrödinger equation for atom-diatom exchange reactions, collision-induced dissociation and related processes have been removed with the result that it has become a viable alternative (and sometimes preferable) to the time-independent route. We seem to be at the threshold of studying three dimensional atom-diatom collisions the time-dependent way. The different computational methods that have made this possible and the applications that have created such an interest are reviewed here.