FIG. 2: Fermi surface of LaO$_{1}$ − $_{x}$F$_{x}$ FeAs. Top-panel: at theoretically optimized position of the As atom with (a) x = 0 and (b) x = 0 . 14. Bottom-panel: at experimental position of the As atom with (c) x = 0 and (d) x = 0 . 14. FIG. 3: Real part of χ ( q , 0) for undoped LaOFeAs (a) on the basal plane (i.e. q$_{z}$ = 0) and (b) on the top plane (i.e. q$_{z}$ = π $_{c}$). 6 A. Static response function Most noticeably the nesting between h -like and e -like FS present in the undoped material becomes less prominent on doping due to the increase in the asymmetry between the e -like and the h -like cylinders. In order to elucidate how this change in FS upon doping manifests itself in the response of the material, in Fig. 3 and 4 are shown the response function χ$_{0}$ ( q , 0) for LaO$_{1}$ − $_{x}$F$_{x}$ FeAs at x = 0 and x = 0 . 14. Looking first at the undoped case, x = 0 (Fig. 3(a)), two main features are clearly visible; first is the presence of a wide flat structure around the Γ and a relatively sharper peak around M point and second is the flatness of the response function in the c -axis (tetragonal axis). As expected, due to the 2D nature of this material similar