Experimental tests for many-body forces in noble gas fluids

Abstract

Effects due to many-body potentials may be studied by comparing the predictions of precise computer simulations (using a good pair potential) with real experimental data. The differences observed may be of almost any relative magnitude, varying with state parameters and other experimental variables. Results of this kind will be discussed regarding P.V.T. data, transport coefficients, and static and dynamic structure factors of noble gas fluids. They are compared to the predictions of a simple mean field model for each effect, in which pair potential simulation is used as the reference system. The model is used as a tool to determine the information content of each property. Reasonable agreement is found for bulk properties, while the extra sensitivity offered by the microscopic data allows a number of deficiencies in the model to be observed. In contrast, a similar series of tests using a computer model, made from the pair potential and the A–T potential in place of the experimental data, shows significantly better overall agreement with the mean field model. This is believed to be due to the neglect of important short range terms in the A–T model. It is concluded that at least three types of many-body forces are important in discussing dense noble gas fluids.