Studies of the thermodynamic and structural properties of liquids by computer simulation

Abstract

Statistical and dynamic simulation computations, on a molecular level, are reported for a variety of simple liquids which are of theoretical or practical interest. Previous work on argon and other group 0 liquids is continued. Thermodynamic contributions from many-body forces are evaluated and the effects of triple-dipole dispersion forces investigated explicitly. The latter results are correlated with liquid microstructure. The Monte Carlo (MC) method of Metropolis et al. and the molecular dynamics (MD) algorithm of Verlet are extended to study dense neutral assemblies of charged particles. Extensive MC calculations for liquid potassium chloride yield the entire equilibrium thermodynamics of the model system. Computed properties are compared with experimental results and the physical approximations of analytical theories, less extensive MD calculations for alkali chlorides (LiCl, NaCl and KC1) are also described. The present MD method suppresses fluctuations in kinetic energy and therby permits isothermal systems to be simulated dynamically. C calculations for the primitive hard-sphere model of electrolyte solutions are reported for a wide range of the reduced variables employed. Computed results are compared with the original Debye-Huckel theory, predictions from the Percus-Yevick and convolution hyper-netted chain integral equations, and experimental heats of dilution and osmotic pressures.Information about the microstructure of simple liquids, liquid mixtures, and fused salts is derived from the equilibrium pair correlation functions. For argon and potassium chloride this is expanded by studying the behaviour of functions describing fluctuations about mean radial number densities. A radial fluctuation function w(r) is introduced and shown to be 1) an important property in the description of liquid microstructure, 2) a useful criterion in selecting the sample size (N) in MC and MD computations, and 3) a means of calculating the isothermal compressibility directly.