Pseudopotential errors in titanium

We present a study of the effect of using different pseudopotentials to represent titanium. We show that apparently arbitrary choices in the reference configuration can lead to significant differences in the calculated quantities. These differences are most striking in the Kohn–Sham “electron” state energies: in structural properties of the solid there is a considerable cancellation of errors. However, 4-electron pseudopotentials with apparently reasonable atomic and scattering properties can give different ground state crystal structures and predict volumes varying by several percent.