A 20 Å vacuum along the c axis was imposed to minimize the interactions of image slabs by periodic condition. Two-dimensional (2D) materials were theoretically exfoliated by extracting one cluster in the standard conventional unit cell of the layered structures screened in the above steps.
Theoretical exfoliation for 2D top-down materials We exclude the compounds with more than 4 elements or 40 atoms in the unit cell.A set of tolerances from 0.0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, to 0.4 was used and only the ones identified as layered by at least two tolerances are left.If the number of clusters in the supercell was three times the ones in the unit cell, the structure was tagged as layered. Make a 3×3×3 supercell and classify all the atoms in the supercell into clusters again.Count the number of clusters in the unit cell. Classify all the atoms in the conventional unit cell into different clusters by checking if they are bonded.If the distance of two atoms smaller than the threshold: boned, else: not bonded. Use a threshold as the sum of the covalent radii of two elements with a small tolerance. Check whether two atoms in the unit cell are bonded or not.
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