There are factors for certain elements which could explain the comparatively weaker Bader charge model performance. The majority of the Ti found in materials are in the oxidation state Ti(IV), and the rising edge energies are sensitive to coordination number . The confluence of these factors could obscure subtle pre-edge trends which correlate with the oxidation state, and help explain the poor Bader charge prediction. It has also been shown that the spin state of Ni and Co atoms can have a great impact on their host geometries : Ni may undergo ligand-based redox in some systems , which leads to little change on the rising edge upon redox state changes while still affecting the underlying charge distributions. This could therefore lead to inaccurate predictions on the Bader charge for Ni. For Cu, the lower performance is possibly due to varied hybridization between Cu and O that affect its oxidation state.