(247i) Assessment and Improvement of Methods for Computing Net Atomic Charges in Periodic and Nonperiodic Materials

Net atomic charges are widely used to concisely convey information about the distribution of electrons among atoms in materials. Here, we compare the performance of various methods for computing net atomic charges in periodic and non-periodic materials. In all, we examined a diverse set of more than a hundred different materials, including molecules, ions, solid surfaces, porous solids, non-porous covalent and ionic solids, organometallic complexes, nanoclusters, nanotubes, monolayer sheets, polymers, and large biomolecules (e.g., DNA). We introduce a new and improved charge assignment method (called DDEC5) whose net atomic charges: (a) have excellent conformational transformability, (b)  follow electronegativity trends, (c) are within a chemically acceptable range (e.g., net atomic charge less than or equal to +1 for Na atoms in materials), (d) approximately reproduce the electrostatic potential surrounding the material, and (e) often correlate to spectroscopically measured core-electron binding energies. These properties make DDEC5 net atomic charges ideally suited for constructing flexible force-fields and for studying the properties of complex materials. In addition, we use this method to compute atomic spin moments in collinear and non-collinear single molecule magnets.