Semiclassical fifth virial coefficients for improved ab initio helium-4 standards

► Tabulate 4th and 5th virial coefficients of He-4 computed using ab initio potentials. ► Evaluate semiclassical treatments of quantum effects for virial coefficients. ► Demonstrate virial equation is more accurate than recent densimeter measurements. ► Advocate use of ab initio results for calibration of apparatus.