  Recent path-integral Monte Carlo and quantum molecular dynamics simulations
have shown that computationally efficient average-atom models can predict
thermodynamic states in warm dense matter to within a few percent. One such
atom-in-jellium model has typically been used to predict the electron-thermal
behavior only, although it was previously developed to predict the entire
equation of state (EOS). We report completely atom-in-jellium EOS calculations
for Be, Al, Si, Fe, and Mo, as elements representative of a range of atomic
number and low-pressure electronic structure. Comparing the more recent method
of pseudo-atom molecular dynamics, atom-in-jellium results were similar:
sometimes less accurate, sometimes more. All these techniques exhibited
pronounced effects of electronic shell structure in the shock Hugoniot which
are not captured by Thomas-Fermi based EOS. These results demonstrate the value
of a hierarchical approach to EOS construction, using average-atom techniques
with shell structure to populate a wide-range EOS surface efficiently,
complemented by more rigorous 3D multi-atom calculations to validate and adjust
the EOS.
