An accurate determination of the liquid structure, dynamics and thermodynamics on the same footing from ab initio molecular dynamics requires particular attention in setting up the electronic structure calculation. Using two well established simulation codes implementing the density functional theory with modern projector augmented wave sets, extensive ab initio molecular dynamics runs have been performed on the CuZr liquid alloy, a prototype of glass-forming alloys. Simulation cells involving about 3000 electrons and energy cutoffs from 285 eV up to 640 eV, well above the values usually taken in simulations of liquid alloys have been used. The influence of the energy cutoff on structural and thermodynamic properties is examined, with a view to estimating the limiting values required for providing reliable reference data for the classical simulations with parametrized force fields. The impact on classi- cal simulations is illustrated with optimized embedded atom model potentials using the force matching method. The various data collected confirm that the ionic pair structure and the diffusion are indeed well converged for energy cutoffs larger than about 285 eV. The greater sensitivity observed for the pressure underlines the neces- sity to pay more attention to the question of incomplete basis set and the structure independent electronic contributions.