4 FIG. 3: (Color online) Static q -dependent Pauli suscepti- bilities at fixed q z = π for (a) LaOFeP and (b) LaOFeAs. The corresponding values of the Pauli susceptibilities at q$_{0}$ = (0 , 0 , π ) in LaOFeP and LaOFeAs, respectively, are sub- tracted. On top, two-dimensional contour maps are shown. Here, GGA is used for the DFT calculations. FIG. 2: (Color online) Fermi surface cuts for (a) LaOFeP and (b) LaOFeAs along different k z -planes, where k z = n/ 4, n ∈ { 0 , 1 , 2 } in units of 2 π . The cyan (light gray) curves are the electron Fermi surfaces around ( π, π, k z ) and the red (dark gray) curves the hole Fermi surfaces around (0 , 0 , k z ). In order to show the nesting properties, the hole Fermi surfaces at (0 , 0 , k z ) are shown again, shifted by ( π, π ). Here we use GGA for the DFT calculations. strates a connection between Fermi surface nesting and magnetism and consequently strongly suggests that the theory of Fermi-surface-nesting-driven magnetism is still valid. In what follows we concentrate on the 1111 compounds and perform a comparative study among LaOFe Pn ( Pn =P, As, Sb, Bi). In Table III and IV, we first present the comparisons of two representative atomic distances among different structures optimized within GGA and experimental structures, if available. Our results agree IV. COMPETITION OF INSTABILITIES IN PAULI SUSCEPTIBILITIES IN 1111 COMPOUNDS TABLE IV: Comparison of representative distances d La-O in ( ˚ A) in LaOFeP, LaOFeAs, LaOFeSb, and LaOFeBi between different GGA optimized structures and experimental struc- tures, if available. TABLE III: Comparison of representative distances d Fe$_{−}$ Pn in ( ˚ A) where P n =P, As, Sb and Bi in LaOFeP, LaOFeAs, LaOFeSb, and LaOFeBi between different GGA optimized structures and experimental structures, if available. Exp. CP-PAW (ours) VASP (ref.) SIESTA 65 LaOFeP 2.350 2.344 2.349 - LaOFeAs 2.363 2.356 2.369 2.374 LaOFeSb - 2.375 2.394 2.398 LaOFeBi - 2.382 - - Exp. 92,93 CP-PAW VASP 89 SIESTA 65 LaOFeP 2.289 2.264 2.232 - LaOFeAs 2.408 2.372 2.357 2.446 LaOFeSb - 2.547 2.50 2.660 LaOFeBi - 2.639 - -