Electronegativity is a key property of the elements. Being useful in rationalizing stability, structure and properties of molecules and solids, it has shaped much of the thinking in the fields of structural chemistry and solid state chemistry and physics. There are many definitions of electronegativity, which can be roughly classified as either spectroscopic (these are defined for isolated atoms) or thermochemical (characterizing bond energies and heats of formation of compounds). The most widely used is the thermochemical Pauling’s scale, where electronegativities have units of eV−1/2. Here we identify drawbacks in the definition of Pauling’s electronegativity scale—and, correcting them, arrive at our thermochemical scale, where electronegativities are dimensionless numbers. Our scale displays intuitively correct trends for the 118 elements and leads to an improved description of chemical bonding (e.g., bond polarity) and thermochemistry.

NaCl is one of the simplest compounds and was thought to be wellunderstood, and yet, unexpected complexities related to it were uncovered at high pressure and in low-dimensional states. Here, exotic hexagonal NaCl thin films on the (110) diamond surface were crystallized in the experiment following a theoretical prediction based on ab initio evolutionary algorithm USPEX. State-of-the-art calculations and experiments showed the existence of a hexagonal NaCl thin film, which is due to the strong chemical interaction of the NaCl film with the diamond substrate.

The hydrogen bond (H-bond) is among the most important noncovalent interaction (NCI) for bioorganic compounds. However, no "energy border" has yet been identified to distinguish it from van der Waals (vdW) interaction. Thus, classifying NCIs and interpreting their physical and chemical importance remain open to great subjectivity. In this work, the "energy border" between vdW and H-bonding interactions was identified using a dimer of water, as well as for a series of classical and nonclassical H-bonding systems. Through means of the quantum theory of atoms in molecules and in particular the source function, it was possible to clearly identify the transition from H-bonding to vdW bonding via analysis of the electronic structure. This "energy border" was identified both on elongating the interatomic interaction and by varying the contact angle. Hence, this study also redefines the "critic angle" previously proposed by Galvão et al. (J. Phys. Chem. A 2013, 117, 12668). Consequently, such "energy border" through an analysis of atomic basins volume variation was possible to identify the end of longrange interactions.

To study the possibility for silicene to be employed as a field-effect transistor (FET) pressure sensor, we explore the chemistry of monolayer and multilayered silicene focusing on the change in hybridization under pressure. Ab initio computations show that the effect of pressure depends greatly on the thickness of the silicene film, but also reveals the influence of real experimental conditions, where the pressure is not hydrostatic. For this purpose, we introduce anisotropic strain states. With pure uniaxial stress applied to silicene layers, a path for sp3 silicon to sp3d silicon is found, unlike with pure hydrostatic pressure. Even with mixed-mode stress (in-plane pressure half of the out-of-plane one), we find no such path. In addition to introducing our theoretical approach to study 2D materials, we show how the hybridization change of silicene under pressure makes it a good FET pressure sensor.

experimental metallization limit moving step by step from 150 [4] to 430-500 GPa. [1,5] A consistent increase in pressure leads to a series of phase transitions in solid hydrogen (phases Ι-V [1,5] ), gradual quenching of the Raman signals, and darkening of the sample down to a complete loss of transparency. Despite a significant progress in achieving ultrahigh pressures in the last five years, detecting superconductivity of metallic hydrogen remains an unsolved problem. Studies of the electrical conductivity at pressures above 400 GPa remain very challenging.In 2004, N. Ashcroft suggested that the precompression effects caused by chemical bonding to other atoms may help to convert hydrogen to a metallic state. Fifteen years later, this idea was confirmed in the synthesis of many metallic and superconducting hydrides such as H 3 S, [6,7] LaH 10 , [8,9] YH 6 , [10,11] YH 9 , [11,12] ThH 10 , [13] CeH 9 , [14] PrH 9 , [15] NdH 9 , [16] and so forth. It is believed now that the superconducting properties of these compounds are due to the presence of a sublattice of metallic hydrogen, which is formed in pure hydrogen only at pressures of 500-700 GPa.There must be an intermediate link between these two forms of hydrogen, metallic and superconducting, and a molecular Recently, several research groups announced reaching the point of metallization of hydrogen above 400 GPa. Despite notable progress, detecting superconductivity in compressed hydrogen remains an unsolved problem. Following the mainstream of extensive investigations of compressed metal polyhydrides, here small doping of molecular hydrogen by strontium is demonstrated to lead to a dramatic reduction in the metallization pressure to ≈200 GPa. Studying the high-pressure chemistry of the Sr-H system, the formation of several new phases is observed: C2/m-Sr 3 H 13 , pseudocubic SrH 6 , SrH 9 with cubic F m 43 -Sr sublattice, and pseudo tetragonal superionic P1-SrH 22 , the metal hydride with the highest hydrogen content (96 at%) discovered so far. High diffusion coefficients of hydrogen in the latter phase D H = 0.2-2.1 × 10 −9 m 2 s −1 indicate an amorphous state of the H-sublattice, whereas the strontium sublattice remains solid. Unlike Ca and Y, strontium forms molecular semiconducting polyhydrides, whereas calcium and yttrium polyhydrides are high-T C superconductors with an atomic H sublattice. The discovered SrH 22 , a kind of hydrogen sponge, opens a new class of materials with ultrahigh content of hydrogen.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202200924.

Crystal structure prediction of new ternary compounds is challenging due to a very large chemical space with many possible compositions, few of which turn out to be stable. Using the evolutionary algorithm USPEX, here we predicted potentially superhard ternary compounds in the W−Mo−B system. Five new stable ternary compounds with various chemical compositions were predicted at different temperatures, and the composition−temperature phase diagrams were calculated. Electronic properties of the new compounds were studied in detail to find their correlation with the mechanical properties, crystal structure, and atomic composition (i.e., mass percentage of elements within the molecular formula).

The source function (SF) is a topological descriptor that was introduced and developed by C. Gatti and R.W. Bader in 1998. The SF describes the contribution of each atom to the total electron density at a given point. To date, this descriptor has only been calculable from electron densities generated by all-electron (AE) methods for the investigation of single molecules or periodic systems. This study broadens the accessibility of the SF, offering its calculation from electron densities generated by plane wave (PW) methods. The new algorithm has been implemented in the open source code, CRITIC2. Our novel approach has been validated on a series of test systems, comparing the results obtained at PW level with those previously obtained through AE methods. © 2016 Wiley Periodicals, Inc.

The theoretical charge density of the active pharmaceutical ingredient piroxicam (PXM) was evaluated through density functional theory with a localized basis set. To understand the electronic nature of the sulfur atom within the sulfonamide group, a highly ubiquitous functional group in pharmaceutical molecules, a theoretical charge density study was performed on PXM within the framework of Bader theory. Focus is on developing a topological description of the sulfur atom and its bonds within the sulfonamide group. It was found that sulfur d-orbitals do not participate in bonding. Instead, the existence of a strongly polarized ("ionic") bonding structure is found through a combined topological and natural bonding orbital analysis. This finding is in stark contrast to long-held theories of the bonding structure of organic sulfonamide and has important implications for the parametrization of calculations using classical approaches.