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In this tutorial we present a tool for predicting the crystal structure of octet binary compounds, by using a set of descriptive parameters (a descriptor) based on free-atom data of the atomic species constituting the binary material.
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In this example, we address only Rocksalt (RS) and Zincblende (ZB) crystal structures, that are the most common for the material class of octet binaries.
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Specifically, the tool predicts the difference in total energy between RS and ZB equilibrated structures (i.e., each structure is relaxed to its local minimum).
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The prediction of RS vs ZB structure from a simple descriptor has a notable history in materials science [1-7], were descriptors were designed by chemically/physically-inspired intuition. The tool presented here allows for the machine-learning-aided automatic discovery of a descriptor and a model for the prediction of the difference in energy between RS and ZB for 82 octet binary materials.
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The tool is based on Compressed-sensing based method (LASSO performed on a tailor-made feature space, followed by L0-regularized minimization, click here for more info on the LASSO+L0 method),
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as introduced in:
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"Big Data of Materials Science: Critical Role of the Descriptor". L. M. Ghiringhelli, J. Vybiral, S. V. Levchenko, C. Draxl, and M. Scheffler Phys. Rev. Lett. 114, 105503 (2015)
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By running the tutorial with the default setting, the results of the PRL 2015 can be recovered. In particular, by clicking on “View interactive 2D plot”, an interactive structure-map (a chart where different structures are located in different regions of a low-dimensional representation, here two dimensional) will be opened in a new tab, similar to the following (a revised version of Fig. 2 in PRL 2015):
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![2016-08-01_ZB_RS3-1](/uploads/44186947a58c4babc13cc9716bd0968d/2016-08-01_ZB_RS3-1.png)
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In this map the octet binaries are located via the descriptor found by our LASSO+L0 approach. The descriptor is based purely on free-atom data, namely radii of the s and p valence orbitals (rs and rp) of the atomic species and their Ionizaiton Potential and Electron Affinity (IP and EA).
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Mateirals in the red (bue) region crystallize preferably in the zincblende (rocksalt) structure. The distance to the green line is proportional to the difference in energy between the two structures.
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In the interactive plot accessible at the end of the learning performed by the present tool, one can obtain information on the materials by hovering and clicking on the data points.
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[1] J. A. van Vechten, Phys. Rev. 182, 891 (1969).
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[2] J. C. Phillips, Rev. Mod. Phys. 42, 317 (1970).
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[3] J. St. John and A.N. Bloch, Phys. Rev. Lett. 33, 1095 (1974).
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[4] J. R. Chelikowsky and J. C. Phillips, Phys. Rev. B 17, 2453 (1978).
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[5] A. Zunger, Phys. Rev. B 22, 5839 (1980).
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[6] D. G. Pettifor, Solid State Commun. 51, 31 (1984).
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[7] Y. Saad, D. Gao, T. Ngo, S. Bobbitt, J. R. Chelikowsky, and W. Andreoni, Phys. Rev. B 85, 104104 (2012).
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