The dynamic properties of monatomic liquids

The computer simulation and inelastic neutron scattering studies of simple, monatomic liquids are reviewed, together with the theory appropriate for their interpretation. Computer simulation (molecular dynamics) studies influenced development of non-equilibrium statistical mechanics techniques for the calculation of correlation functions that enter the various measured susceptibilities. Studies of systems interacting via continuous potentials have developed to a high level of sophistication. Neutron scattering experiments are difficult to perform with high accuracy, yet offer a unique means of investigating the dynamics of simple liquids in the domain of wavevectors and frequencies larger than about 0.05 AA-1 and 5*1011 s-1 respectively. The problems faced in analysing neutron data to the level required are reviewed in detail. Theory has developed through the rigorous generalization of the Markovian theory of fluctuations set out by Landau and Lifshitz (1959). The development has taken the form of a generalized Langevin equation, which provides a framework within which neutron and molecular dynamics data may be interpreted.