Karl-Erik Larsson

The structure factor for liquid lead

Abstract The structure factor for liquid lead at the temperatures 613 K, 643 K, 863 K and 1163 K are measured by neutron diffraction. Extensive comparisons to earlier measurements are made as well as comparisons to different hard-core models.

Review article: some transport phenomena in classical liquids and neutron scattering

Abstract Our knowledge in liquid physics and particularly in the field of nonb-equilibrium phenomena has increased enormously during the last two decades. The raason are two-fold: (a) the application of the slow neutron inelastic scatteing technique to the liquid state has supplied us with very valuable fundamental data and has stimulated theoretical work and (b) the applicaiton of molecular dynamics computations to problems of liquid dynamics has profoundly deepened dour understanding of fundamental dynamical quantities. The combination of the two ways of research has shown how to approach the solutionof clasical questions: For instance to what small wave length domain may we apply the normal hydrodynamical equations? And When these eequations cease to exist what would be a good theoretival continuaion into the short wave length domain? The modern techniques hav shown that normal hydrodynamic is useful down to wave lengths approximately ten atomic distances. Thereafter kinetic efffects of atomic nature t...

Liquid atomic motions from line width studies of scattering functions s(k,ω) and ss (k,ω)

Abstract In recent years accurate experimental values of the FWHM (full width at half maximum) of the scattering functions S(k,ω) were published. Similarly molecular dynamics studies were produced for the corresponding widths for self motion for liquid argon and rubidium. Combining knowledge from these two fields sheds some new light on the connections between self motion and collective motions in the liquids. In the present work four fluids are considered, namely argon, rubidium, lead and bismuth. It is argued that the study of these line widths gives considerable insight into the nature of the self diffusion process even if the wave vectors involved are such that k > ko, where kO, is the wave vector value at which the liquid structure factor has its main maximum. Effects of self motion dominate in this region. When k < kO the collective effects in S(k, ω) dominate completely and the importance of self motion disappears as k → 0.

Atomic self-motion in liquid lead: mode-coupling analysis and evidence for structural effects in self-diffusion

Atomic self-motion in liquid lead at 623 K and 1170 K was studied by MD simulation using a system of 16 384 particles. The simulation was based on the effective pair potential derived earlier from the measured structure factor.

Comparison of the results of mode-coupling theory for liquid lead at 623 K and 1170 K with molecular dynamics data

Abstract The mode-coupling formalism for the memory function of the velocity autocorrelation function formulated roughly 10 years ago by Sjolander, Sjogren and Wahnstrom is believed to describe the dynamical properties of argon and rubidium in the liquid state relatively well. Moreover, mode-coupling theory has been successfully applied to interpret a number of dynamical phenomena observed in a supercooled liquid approaching the liquid-glass transition. The results of a mode-coupling theory limited to four coupling terms and extended to Q -dependent memory functions over the region of 0–6 A −1 are discussed. The comparison with molecular dynamics (MD) data demonstrates that mode-coupling theory overestimates the long-time tail of the second-order memory function and fails to describe correctly the self-motion of liquid lead both at low and high temperature. The self-diffusion coefficient obtained from a mode-coupling calculation is about 25% too low. However, the analysis of the results at two different temperatures indicates that there is a systematic pattern in the discrepancies which suggests a possibility to improve the theoretical approach to match the MD-results.