Introducing DDEC6 atomic population analysis: part 2. Computed results for a wide range of periodic and nonperiodic materials

Abstract

Net atomic charges (NACs) are widely used throughout the chemical sciences to concisely summarize key information about charge transfer between atoms in materials. The vast majority of NAC definitions proposed to date are unsuitable for describing the wide range of material types encountered across the chemical sciences. In this article, we show the DDEC6 method reproduces important chemical, theoretical, and experimental properties across an extremely broad range of material types including small and large molecules, organometallics, nanoclusters, porous solids, nonporous solids, and solid surfaces. Some important comparisons we make are: (a) correlations between various NAC models and spectroscopically measured core-electron binding energy shifts for Ti-, Fe-, and Mo-containing solids, (b) comparisons between DDEC6 and experimentally extracted NACs for formamide and natrolite, (c) comparisons of accuracy of different NAC methods for reproducing the electrostatic potential surrounding a material across one and multiple system conformations, (d) comparisons between calculated and chemically expected electron transfer trends for atoms in numerous dense solids, solid surfaces, and molecules, (e) an assessment of NAC transferability between three crystal phases of the diisopropylammonium bromide organic ferroelectric, and (f) comparisons between DDEC6 and polarized neutron diffraction atomic spin moments for the Mn 12 -acetate single-molecule magnet. We find the DDEC6 NACs are ideally suited for constructing flexible force-fields and give reasonable agreement with force-fields commonly used to simulate biomolecules and water. We find the DDEC6 method is more accurate than the DDEC3 method for analyzing a broad range of materials. This broad applicability to periodic and non-periodic materials irrespective of the basis set type makes the DDEC6 method suited for use as a default atomic population analysis method in quantum chemistry programs. † Electronic supplementary information (ESI) available: Tables listing spectroscopically measured core electron energies and Bader, CM5, DDEC3, DDEC6, HD NACs for Ti-and Mo-containing solids; plot comparing DDEC6 to DDEC3 NACs for 14 systems comprised almost entirely of surface atoms; DDEC6 and DDEC3 NACs for Mo 2 C(110) surface with K adatom and NaF (001) surface; DDEC6 and DDEC3 NACs, atomic dipoles, and atomic quadrupoles for SrTiO 3 (100) surface and bulk crystal; DDEC6, DDEC3, Bader, and IH NACs for NaF and SrTiO 3 bulk crystals; xyz les (which can be read using any text editor or the free Jmol visualization program downloadable from jmol.sourceforge.net) containing geometries, NACs, atomic dipoles and quadrupoles, tted tail decay exponents, and ASMs. See

Introducing DDEC6 atomic population analysis: part 1. Charge partitioning theory and methodology

“…33 The target values for tests 6, 7, and 8 (molecules) are charges that will more closely reproduce the electrostatic potential and were chosen to approximate ESP charges. 33 The target values for tests 6, 7, and 8 (molecules) are charges that will more closely reproduce the electrostatic potential and were chosen to approximate ESP charges.…”

“…For these applications, the NACs should approximately reproduce the molecular electrostatic potential (MEP). 19,33 The Li 2 O conformations span angles from 90 to 180 in 10 increments. Table 4 compares the accuracy of the DDEC6 and Convex functional methods for reproducing the electrostatic potential across various conformations of carboxylic acids, Li 2 O molecule, and Zn-nicotinate metal-organic framework.…”

“…Conformational transferability is important for the construction of exible force-elds. 33 The Zn-nicotinate conformations are described in Section 5.3. Results listed under the 'carboxylic acids' column in Table 4 are the averages for the previously published conformations of ve carboxylic acids.…”

“…33 Third, the correlation between NACs and core electron binding energy shis will be weakened due to the overly delocalized assignment of electrons to the anions (see Ti-containing compounds in Table 3). In dense materials, the diffuse nature of anions can cause the number of electrons assigned to an anion to be much greater than the number of electrons in the volume dominated by the anion.…”

“…(7) The Natural Population Analysis (NPA), 8 Natural Bond Orbital (NBO), 26 Adaptive Natural Density Partitioning (ANDP), 27 Intrinsic Atomic Orbital, 28 Intrinsic Bond Orbital, 28 and several related approaches 29 provide chemically meaningful localized atomic and bonding orbitals. 33 This scientic engineering design approach requires choosing performance goals. In the near future, modications of some of these methods might emerge with sufficiently wide applicability and convergence robustness to be used as default methods in quantum chemistry programs.…”