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

For helium-4, we present ab initio, semiclassical calculations of virial coefficients Bn for n = 2, 3, 4, and 5 from 50 to 1000 K. Using our values of B4 and B5 and the more accurate literature values of B2 and B3, we argue that the ab initio virial equation of state is more accurate than recent, high-quality, densimeter measurements spanning the range {223 K < T < 500 K, p < 38 MPa}. Thus, the present values of B4 and B5 extend the useful temperature and density range of ab initio helium standards.