Improved First-Principles Calculation of the Third Virial Coefficient of Helium
Giovanni Garberoglio, Michael R. Moldover, Allan H. Harvey
We employ state-of-the-art pair and three-body potentials for helium to calculate its third density virial coefficient C(T) with uncertainties 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 which become important below approximately 7 K. Results are given for both the 3He and 4He isotopes. We have also calculated the third acoustic virial coefficient (gamma)a; our calculated values compare well with the limited experimental data available. A correlating nist-equation for C(T) of 4He is presented; differentiation of this nist-equation provides a reliable and simpler way of calculating (gamma)a.