tent with the experimental one. According to the re- lation we fitted, LaOFeSb always gives the highest T$_{c}$ of 57.5 (50.6) K for LDA (GGA) optimizations, respectively, among the four 1111 compounds we studied. Combining the two presented phenomenological prediction schemes, we clearly obtain that LaOFeSb would be upon doping or under pressure a good candidate for superconductivity with highest T$_{c}$ and it would be very interesting to see it synthesized. 

In the present work we studied the physical proper- ties of LaOFe P n , BaFe$_{2}$ P n$_{2}$ and LiFe P n with P n =As and Sb. Our results support the validity of the itin- erant nature of magnetism in these compounds where magnetization is closely related to Fermi surface nest- ing. Furthermore, we concentrated on the 1111 com- pounds LaOFe P n with P n =P, As, Sb, and Bi. We found that the increase of the magnetic moment in the undoped compounds with P n varying from P to Bi is due to the increasing instability of the Pauli suscep- tibility at q$_{π}$ = ( π, π, π ) and the decreasing competi- tion to the instability at q$_{0}$ = (0 , 0 , π ). The supercon- ducting state appearing in undoped LaOFeP at ambi- ent pressure is ascribed to the strong competition be- tween the instability at q$_{π}$ = ( π, π, π ) and q$_{0}$ = (0 , 0 , π ). Thus, together with the investigation of the DOS in the 

1 Y. Kamihara, T. Watanabe, M. Hirano, and H. Hosono, J. Am. Chem. Soc. 130 , 3296 (2008). 2 

Z. A. Ren, W. Lu, J. Yang, W. Yi, X. L. Shen, Z. C. Li, G. C. Che, X. L. Dong, L. L. Sun, F. Zhou, and Z. X. Zhao, Chin. Phys. Lett. 25 , 2215 (2008). 3 

Milton S. Torikachvili, Sergey L. Bud’ko, Ni Ni, and Paul C. Canfield, Phys. Rev. Lett. 101 , 057006 (2008). 4 

K. Sasmal, B. Lv, B. Lorenz, A. M. Guloy, F. Chen, Y. Xue and P. C. W. Chu, Phys. Rev. Lett. 101 , 107007 (2008). 5 

G. F. Chen, Z. Li, G. Li, Z. Hu, J. Dong, X. D. Zhang, P. Zheng, N. L. Wang and J. L. Luo, Chin. Phys. Lett. 25 , 3403 (2008). 6 

M. Rotter, M. Tegel and D. Johrendt, Phys. Rev. Lett. 101 , 107006 (2008). 7 

P. L. Alireza, Y. T. C. Ko, J. Gillett, C. M. Petrone, J. M. Cole, G. G. Lonzarich and S. E. Sebastian, J. Phys.: Condens. Matter 21 , 012208 (2009). 8 

S. A. J. Kimber, A. Kreyssig, Y.-Z. Zhang, H. O. Jeschke, R. Valent´ı, F. Yokaichiya, E. Colombier, J. Yan, T. C. Hansen, T. Chatterji, R. J. McQueeney, P. C. Canfield, A. I. Goldman and D. N. Argyriou, Nature Materials 8 , 471 (2009). 9 

A. S. Sefat, R. Jin, M. A. McGuire, B. C. Sales, D. J. Singh, and D. Mandrus, Phys. Rev. Lett. 101 , 117004 (2008). 10 

X. C. Wang, Q. Liu, Y. Lv, W. Gao, L. X. Yang, R. C. Yu, F. Y. Li, and C. Jin, Solid. State. Commun. 148 , 538 

## VI. CONCLUSIONS 

low temperature phase, we argue that the hypotheti- cal compounds LaOFeSb and LaOFeBi are antiferromag- netic metals at ambient pressure without doping. The results for LaOFe P n again strongly imply that Fermi surface nesting plays a dominating role in the physical properties of the 1111 compounds. Finally we consider two phenomenological relations to predict the supercon- ducting transition temperature T$_{c}$ for the hypothetical 1111 compounds and predict that LaOFeSb would be a possible candidate for a superconductor with a higher T$_{c}$ than presently recorded for the known Fe-based su- perconductors. Combining the fact that Fermi surface nesting dominates the physics in the 122 compounds, 1111 compounds, 11 compounds, and 111 compounds, we argue that magnetism in iron-based superconductors is strongly influenced by their itinerant nature. However, from our study, the localized scenario is not ruled out and may also play an important role in the physics of iron- based superconductors. Furthermore, while in our study we emphasize the role of the states at the Fermi level and accordingly the nesting property of the Fermi surface on the itinerant nature of magnetism, the significant contri- butions to the finite moment of itinerant magnetism from the states in the vicinity of the Fermi level should not be ignored. 

Acknowledgments.- We would like to thank the Deutsche Forschungsgemeinschaft for financial support through the SFB/TRR 49 and Emmy Noether programs. 

(2008) 

11 J. H. Tapp, Z. Tang, B. Lv, K. Sasmal, B. Lorenz, P. C. W. Chu, and A. M. Guloy, Phys. Rev. B 78 , 060505 (2008). 12 

M. J. Pitcher, D. R. Parker, P. Adamson, S. J. C. Herkel- rath, A. T. Boothroyd, R. M. Ibberson, M. Brunelli, and S. J. Clarke, Chem. Commun. 2008 , 5918 (2008). 13 

S. J. Zhang, X. C. Wang, R. Sammynaiken, J. S. Tse, L. X. Yang, Z. Li, Q. Q. Liu, S. Desgreniers, Y. Yao, H. Z. Liu, and C. Q. Jin, Phys. Rev. B 80 , 014506 (2009). 14 

D. R. Parker, M. J. Pitcher, P. J. Baker, I. Franke, T. Lan- caster, S. J. Blundell, and S. J. Clarke, Chem. Commun. (Cambridge) ( 2009 ), 2189. 15 

G. F. Chen, W. Z. Hu, J. L. Luo, and N. L. Wang, Phys. Rev. Lett. 102, 227004 (2009). 16 

F.-C. Hsu, J.-Y. Luo, K.-W. Yeh, T.-K. Chen, T.-W. Huang, P. M. Wu, Y.-C. Lee, Y.-L. Huang, Y.-Y. Chu, D.-C. Yan, and M.-K. Wu, Proc. Natl. Acad. Sci. U.S.A. 105 , 14262 (2008). 17 

Y. Mizuguchi, F. Tomioka, S. Tsuda, T. Yamaguchi, and Y. Takano, Appl. Phys. Lett. 93 , 152505 (2008). 18 

K.-W. Yeh, T.-W. Huang, Y. lin Huang, T.-K. Chen, F.- C. Hsu, P. M. Wu, Y.-C. Lee, Y.-Y. Chu, C.-L. Chen, J.-Y. Luo, D.-C. Yan, and M.-K. Wu, Europhys. Lett. 84 37002 (2008). 19 

H. Q. Yuan, J. Singleton, F. F. Balakirev, S. A. Baily, G. F. Chen, J. L. Luo, N. L. Wang, Nature 457 , 565 (2009). 20 

D. J. Singh and M.-H. Du, Phys. Rev. Lett. 100 , 237003 

