title: Improved First-Principles Calculation of the Third Virial Coefficient of Helium.
abstract: We employ state-of-the-art pair and three-body potentials with path-integral Monte Carlo (PIMC) methods to calculate the third density virial coefficient C(T) for helium. The uncertainties are much smaller than those of the best experimental results, and approximately one-fourth the uncertainty of our previous work. We have extended our results in temperature down to 2.6 K, incorporating the effect of spin statistics that become important below approximately 7 K. Results are given for both the (3)He and (4)He isotopes. We have also performed PIMC calculations of the third acoustic virial coefficient γ a; our calculated values compare well with the limited experimental data available. A correlating equation for C(T) of (4)He is presented; differentiation of this equation provides a reliable and simpler way of calculating γ a.
authors.affiliation: Interdisciplinary Laboratory for Computational Science (LISC), FBK-CMM and University of Trento, Via Sommarive 18, I-38123 Povo, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Garberoglio
authors.affiliation: Temperature, Pressure, and Flow Metrology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Moldover
authors.affiliation: Thermophysical Properties Division, National Institute of Standards and Technology, Boulder, CO 80305.
authors.forename: Allan H
authors.initials: AH
authors.lastname: Harvey
keywords: calibration; coustic virial coefficients; density; helium; metrology; thermodynamic properties; virial coefficients