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There are several open questions. What is the effect of U on the energy landscape. Does U simply shift the local minima relative to one another, or does it create and destroy minima? Additionally, when is U necessary for correct reordering of the candidate energies? Perhaps U is only necessary for compound containing correlated atoms, or magnetic materials. Larger scale studies on multiple keystone compositions is necessary.  In conclusion, or our  proposed strategy for structural prediction is as follows: first perform USPEX runs with spin-polarized DFT to generate the list of structures occupying local minima in the energy landscape. Then, apply LDA+U to the resulting structures to reorder the total energies to determine the true ground state structure. This is more economical than running USPEX with hundreds of calls to LDA+U, since LDA+U is more expensive than LDA. [Ran, could you estimate the difference in running time between your proposed re-ordering algorithm vs. the naive USPEX LDA+U run?] \emph{Global stability} -- Since the material was known to exist, we did not construct the convex hull and check for global thermodynamic stability. [Maybe we should do this. What do you think, Gabi?]