Ab initio potentials and the equation of state of condensed helium at high pressure

The equation of state of condensed He-4, at room temperature and at pressures between similar to 10 and similar to 50 GPa, is computed by Path Integral Monte Carlo simulations. Recently proposed, ab initio pair and three-body potentials are utilized. Results are compared to available experimental data, as well as to predictions obtained with two- and three-body potentials used in previous studies. If only two-body interactions are included, the pressure is overestimated by as much as 56% at the highest compression considered here. A relatively modest improvement is offered by the recently developed SAPT over the more commonly adopted Aziz potential. The introduction of three-body forces, modeled using two different potentials, causes instead a significant underestimation of the pressure. In the range of density explored here, agreement with experiment cannot be obtained simply by rescaling the strength of the attractive part of the three-body potential, as had been empirically found in previous work. The results suggest that either four-body terms are more important than previously thought, or, possibly, that the entire approach based on a static potential may be inadequate. Three-body forces are found to have a negligible effect on structural properties and on the single-particle kinetic energy, for which estimates are provided. (C) 2001 American Institute of Physics.