Brillouin scattering and three-body forces in argon at high pressures

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Abstract
Brillouin scattering was measured at room temperature in liquid and solid argon in a diamond-anvil cell at pressures up to 33 GPa. In the fluid, our results agree well with those obtained by ultrasonic methods. In the solid, the elastic anisotropy and the use of the experimental equation of state allowed us to determine limiting values for all the elastic constants as a function of pressure. We also performed self-consistent phonon calculations using various pair potentials proposed for argon. From the comparison between calculation and experiment it can be stated that in dense solid argon there is no way to reproduce the experimental results with any pair potential and that many-body exchange potentials have to be incorporated for an accurate description.