The characterization of bonding interactions in molecules and materials is one of the major applications of quantum mechanical calculations. Numerous schemes have been devised to identify and visualize chemical bonds, including the electron localization function, quantum theory of atoms in molecules, and natural bond orbital analysis, whereas the energetics of bond formation are generally analyzed in qualitative terms through various forms of energy partitioning schemes. In this Article, we illustrate how the chemical pressure (CP) approach recently developed for analyzing atomic size effects in solid state compounds provides a basis for merging these two approaches, in which bonds are revealed through the forces of attraction and repulsion acting between the atoms. Using a series of model systems that include simple molecules (H, CO, and S), extended structures (graphene and diamond), and systems exhibiting intermolecular interactions (ice and graphite), as well as simple representatives of metallic and ionic bonding (Na and NaH, respectively), we show how CP maps can differentiate a range of bonding phenomena. The approach also allows for the partitioning of the potential and kinetic contributions to the interatomic interactions, yielding schemes that capture the physical model for the chemical bond offered by Ruedenberg and co-workers.

The crystal structure of many inorganic compounds can be understood as a metallic matrix playing the role of a host lattice in which the nonmetallic atomic constituents are located, the Anions in Metallic Matrices (AMM) model stated. The power and utility of this model lie in its capacity to anticipate the actual positions of the guest atoms in inorganic crystals using only the information known from the metal lattice structure. As a pertinent test-bed for the AMM model, we choose a set of common metallic phases along with other nonconventional or more complex structures (face-centered cubic (fcc) and simple cubic Ca, CsCl-type BaSn, hP4-K, and fcc-Na) and perform density functional theory electronic structure calculations. Our topological analysis of the chemical pressure (CP) scalar field, easily derived from these standard first-principles electronic computations, reveals that CP minima appear just at the precise positions of the nonmetallic elements in typical inorganic crystals presenting the above metallic subarrays: CaF 2 , rock-salt, and CsCl-type phases of CaX (X = O, S, Se, Te), BaSnO 3 , K 2 S, and NaX (X = F, Cl, Br, I). A theoretical basis for this correlation is provided by exploring the equivalence between hydrostatic pressure and the oxidation (or reduction) effect induced by the nonmetallic element on the metal structure. Indeed, our CP analysis leads us to propose a generalized stress-redox equivalence that is able to account for the two main observed phenomena in solid inorganic compounds upon crystal formation: (i) the expansion or contraction experienced by the metal structure after hosting the nonmetallic element while its topology is maintained and (ii) the increasing or decreasing of the effective charge associated with the anions in inorganic compounds with respect to the charge already present in the interstices of the metal network. We demonstrate that a rational explanation of this rich behavior is provided by means of Pearson-Parr's electronegativity equalization principle. INTRODUCTIONThe literature on the theories and formalisms describing chemical bonding in inorganic crystal structures is very extensive, 1−6 and the models can typically be classified into either classical or quantum types. Among them, the approach of Pauling has been the paradigm for describing and rationalizing the crystal structures of ionic compounds over the last century. 7,8 The limitations of the ionic model, which have also led to a number of misconceptions about the crystal structure and the bonding network, were discussed by O'Keeffe and Hyde using alternative approaches. 9,10 These authors put the emphasis on the description of the structures of oxides as oxygen-stuffed alloys, since their cationic sublattices adopt the structures of either elements or simple alloys. Interestingly, this concept can also be applied to the naked metallic structure if the valence electrons localized in the empty spaces of the structure are conceived as coreless 49 pseudoanions. In fact, the term electride was introduced af...

Bond and lone pairs are identified by the Chemical Pressure formalism providing correlations between ligand electronegativity and molecular activity within the VSEPR-LCP model.