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Electrostatic potential in crystals of α-boron, γ-boron and boron carbide

Abstract An overview is given of the recently proposed method for computation of the electrostatic potential (ESP) of dynamic charge densities derived from multipole models [C. B. Hubschle, S. van Smaalen, J. Appl. Crystallogr.2017, 50, 1627]. The dynamic ESP is presented for the multipole models of the boron polymorphs α-B12 and γ-B28, and stoichiometric boron carbide B13C2. Minimum values of the ESP are conspiciously equal at approximately −1 electron/Å. Regions with the ESP close to its minimum value form an extended network throughout the crystal structures at locations far away from atoms and bonds. Boron and boron carbide are extended solids containing an infinite network of strong chemical bonds. We have shown that for such solids, the ESP can usefully considered on Hirshfeld surfaces encompassing groups of atoms. Accordingly, we discuss bonding in boron and boron carbide with aid of the ESP on the Hirsfeld surface encompassing a B12 icosahedral cluster. The structure of the ESP corroborates the interpretation of the bonding characteristics previously proposed for α-B12, γ-B28 and B13C2.