Extending Linear Response: Inferences from Electron-Ion Structure Factors

Linear response methods applied to electron systems often display a level of accuracy which is notable when viewed in terms of the strengths of perturbing interactions. Neglect of higher response terms is in fact justifiable in many cases and it can be shown to stem from an intrinsic interference between atomic and electronic length scales. For fluid metallic systems it can be further shown that electron-ion structure (increasingly accessible experimentally) can be understood from an application of linear response in the electron system, combined with hard-sphere like correlation for the ionic component.