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In Fig. 7, we plot χ ( π, π, π ) − χ (0 , 0 , π ) versus T$_{c}$ for the hypothetical 1111 compounds LaOFeSb, LaOFeBi, ScOFeP and ScOFeAs. The phenomenological relation between T$_{c}$ and χ ( π, π, π ) − χ (0 , 0 , π ) is determined by first calculating χ ( π, π, π ) χ (0 , 0 , π ) for several typ- ical 1111 compounds LaOFeP $^{90,92}$, LaOFeAs$^{1,93}$, Ce- OFeAs $^{94,95}$, NdOFeAs$^{96,97}$, and SmOFeAs$^{98,99}$, where T$_{c}$ and lattice structures are given experimentally, and then fitting the data by an exponential growth function of χ ( π, π, π ) − χ (0 , 0 , π ) = 2 . 86+0 . 28 ∗ exp( T$_{c}$/ 18 . 14). With this relation, Tc for the compounds which have not yet been experimentally reported is predicted by optimizing the lattice structure and calculating χ ( π, π, π ) − χ (0 , 0 , π ) from DFT calculations. From Fig. 7, we find that the re- sulting χ ( π, π, π ) − χ (0 , 0 , π ) for LaOFeP and LaOFeAs based on our optimized structures is only slightly under- estimated compared to that calculated from experimen- tal structures, which shows that the result depends only weakly on our structure optimization. Among the four 1111 compounds, this procedure shows that LaOFeSb can give the highest T$_{c}$ around 60 K which is above the highest recorded T$_{c}$ of 55 K in SmOFeAs. 

An alternative procedure to predict T$_{c}$ phenomenolog- ically is based on the fact that the physical properties 

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of Fe-based superconductors strongly depend on the As position. Tiny shiftings of the As position away from or closer to the iron plane will significantly change the band structure around the Fermi level $^{20,88}$. Therefore, similar to Refs. 95 and 100, we plot in Fig. 8 T$_{c}$ versus the absolute value of the ratio between atomic distances d$_{Fe-Fe}$ and d$_{Fe-As}$ while subtracting r$_{0}$ = d$_{0}$$_{,}$$_{Fe-Fe}$/d$_{0}$$_{,}$$_{Fe-As}$ where d$_{0}$$_{,}$$_{Fe-Fe}$ and d$_{0}$$_{,}$$_{Fe-As}$ denote the distances in a perfect tetrahedron formed by four nearest neighbor As atoms surrounding one Fe atom. Similar to the first scheme, we determine the phenomenological relation be- tween | d$_{Fe-Fe}$/d$_{Fe-As}$ − r$_{0}$ | and T$_{c}$ by taking into account the same compounds LaOFeP, LaOFeAs, CeOFeAs, Nd- OFeAs, and SmOFeAs as in the first scheme where T$_{c}$ and lattice structures are given experimentally and do- ing a linear fit as in Ref. 95. With this relation, the T$_{c}$ for LaOFeSb, LaOFeBi, ScOFeP and ScOFeAs is predicted based on the optimized structure. 

Fig. 8 presents the results based on the structures op- timized within both GGA and LDA. Comparing the re- sults for LaOFeP and LaOFeAs from GGA and LDA op- timizations with those from experiments, we find that the optimized structures from GGA are more consis- 

