  The low-density limit of the electrical conductivity $\sigma(n,T)$ of
hydrogen as the simplest ionic plasma is presented as function of temperature T
and mass density n in form of a virial expansion of the resistivity. Quantum
statistical methods yield exact values for the lowest virial coefficients which
serve as benchmark for analytical approaches to the electrical conductivity as
well as for numerical results obtained from density functional theory based
molecular dynamics simulations (DFT-MD) or path-integral Monte Carlo (PIMC)
simulations. While these simulations are well suited to calculate $\sigma(n,T)$
in a wide range of density and temperature, in particular for the warm dense
matter region, they become computationally expensive in the low-density limit,
and virial expansions can be utilized to balance this drawback. We present new
results of DFT-MD simulations in that regime and discuss the account of
electron-electron collisions by comparing with the virial expansion.
