Raman scattering in hcp rare gas solids under pressure

We present Raman measurements of hcp rare gas solids (RGSs) at megabar pressures together with lattice dynamics calculations. The E(2g) phonon was measured in Xe up to metallization near 135 GPa and in Ar up to 58 GPa. A comparative analysis of first-principles and semiempirical calculations shows that three-body forces contribute to the energetics at low pressures and that at volume compressions greater than similar to 2.6 higher-order many-body forces become important. The distinct behavior of He under pressure relative to that of the rest of the RGS family is discussed.