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of LaOFeAs calculated using both z$_{As}$ are shown in Fig. 1. Four bands cross the Fermi level E$_{F}$ , having predominantly Fe d character moderately hybridized with As p . These band structures are in agreement with previous results $^{16,25}$. 

The corresponding FS are given in Fig. 2. The FS calculated with optimized and exper- imental z$_{As}$ for the undoped compound are quite similar with two e -like cylinders around the M point and two h -like cylinders warped around the Γ point of the BZ. However, the two FS differ when it comes to the third h -like manifold which appears as a 3D structure on the use of optimized As positions and as a 2D cylinder when the experimental atomic positions are used. 

Since the parent compound becomes superconducting on electron doping, it is important to look at the change in the electronic structure as a function of the Fluorine content. 

The doping is treated by the means of rigid band model (RBM) which is a reasonable approximation for LaOFeAs $^{28}$. As for the crystal structure, it is kept fixed to the undoped values even for the doped case. This choice is justified for the material under investigation; it was shown by Mazin et al. 25 that the lattice parameter and atomic positions are not sensitive to the doping. The FS for the 14% doped compound is shown in Fig. 2. Even though the undoped FS calculated using optimized and experimental z$_{As}$ are substantially different, the doped FS for the two cases are fairly similar. The h -like FS sheet around Γ point for x = 0 quickly disappears on electron doping in both cases ( z$_{As}$ optimized and experimental) with only 2D tubular structures around the Γ − Z ( h -like) and the M − A ( e -like) lines surviving. 

