Chuck-Hou Yee edited bacoso2.tex  over 7 years ago

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In order to not miss crucial seed structures which ultimately led to the experimental structure, we found that the randomly generated initial population of structures must be sufficiently large. An initial population of size 300 was sufficient with a single generation size of 60. In total $\sim 700$ metastable structures were produced in 8 generations. In addition, spin polarization is crucial for the local relaxations performed within each USPEX generation in order to find the experimental structure. When non-spin-polarized DFT was used, we could not find some of the lowest energy materials (including the observed structure)  What causes the relative shift in energies as function of U? We first roughly grouped the structures by the behavior of the $E$ vs. $U-J$ curve, which we have indicated by colors in Fig.~\ref{fig:reordering}.  Roughly, the correction depends on the occupation of the 3d orbitals to which U is applied, namely the energy difference between two states with occupations n1 and n2 is roughly $∆E \sim U(n1-1/2)(n2-n1)$. [Gabi, Ran, this is just my hypothesis. Ran, could you check this from the data?] We can classify the candidate structures by the evolution of their energies as a function of U into roughly three groups. The largest group has a slope of roughly $∆E \sim 0.3U$. A second subset has energies that a relatively constant $(∆E \sim const)$. The third group, which appeared to have the lowest energies in the U = 0 run, rapidly increases in energy with $∆E \sim 0.7U$. We can rationalize this behavior by [need to look at the data here — maybe it has to do with the local ligand environment of the Co atom, and maybe we won’t be able to rationalize it.]