Ab initio potentials and the equation of state of condensed helium at highpressure

The equation of state of condensed He-4, at room temperature and at pressur es between similar to 10 and similar to 50 GPa, is computed by Path Integra l Monte Carlo simulations. Recently proposed, ab initio pair and three-body potentials are utilized. Results are compared to available experimental da ta, as well as to predictions obtained with two- and three-body potentials used in previous studies. If only two-body interactions are included, the p ressure is overestimated by as much as 56% at the highest compression consi dered here. A relatively modest improvement is offered by the recently deve loped SAPT over the more commonly adopted Aziz potential. The introduction of three-body forces, modeled using two different potentials, causes instea d a significant underestimation of the pressure. In the range of density ex plored here, agreement with experiment cannot be obtained simply by rescali ng the strength of the attractive part of the three-body potential, as had been empirically found in previous work. The results suggest that either fo ur-body terms are more important than previously thought, or, possibly, tha t 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.