Refining Fermi surface topologies from ab initio calculations through momentum density spectroscopies

It is well known that the agreement between the Fermi surface topologies predicted by ab initio electronic structure calculations and experiment can often be brought into much better agreement through small rigid-band-like shifts. A new method for refining these calculations using experimental data containing Fermi surface information, based on a rigid-band-like fitting approach is presented. In this method, experimental data from different methods can be combined to refine and deliver a ‘tuned’ bandstructure, allowing an investigation of FS nesting properties, a quantitative comparison between experiment and calculation, and highlighting the origin of inconsistencies. Results of the application of this method to positron annihilation experiments in vanadium are presented, showing significant improvement over the ab initio calculation. In order to demonstrate the versatility of this fitting method, it has been applied to a combination of positron annihilation measurements and magnetic Compton scattering experiments in ferromagnetic nickel.