Efficient calculation of the structural and electronic properties of mixed valence materials: application to Prussian Blue analogues

Mixed valence materials containing the same atom type in different spin and/or oxidation states, although displaying great applications potential, present a considerable challenge to accurate efficient electronic structure calculations employing ultra-soft pseudo-potentials (USPPs). Ideally USPPs should aim for full transferability between all centres of the same atom type. Via examining an archetypal class of mixed valence materials (Prussian Blue analogues) we show: (i) using a single USPP appears be a non-transferable approach for the mixed valence centres and (ii) such materials can be treated via a mixed-USPP approach whereby each mixed valence centre type is assigned a suitable USPP.