Valence (chemistry)

About: Valence (chemistry) is a research topic. Over the lifetime, 24937 publications have been published within this topic receiving 645252 citations. The topic is also known as: valency.

Structures and Bond Energies of the Transition Metal Hexacarbonyls M(CO)6 (M = Cr, Mo, W). A Theoretical Study

Abstract: The geometries of the hexacarbonyls and pentacarbonyls of chromium, molybdenum, and tungsten are optimized at the Hartree-Fock and ML2 levels of theory using effective core potentials for the metal atoms. The M-CO bond lengths of Mo(CO) 6 and W(CO) 6 predicted at the ML2 level using moderate valence basis sets are in excellent agreement with experimental values. The Cr-CO bond length in Cr(CO) 6 calculated at ML2 is too short. The total bond energies of the metal hexacarbonyls calculated at the CCSD(T) level of theory are slightly lower than the experimentally derived values

Noncovalent functionalization of carbon nanotubes by aromatic organic molecules

Abstract: The interaction between carbon nanotubes and organic molecules including benzene (C6H6), cyclohexane (C6H12), and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ: C8N2O2Cl2) have been studied using first principles calculations. The equilibrium tube-molecule distance, adsorption energy, and charge transfer are obtained. The hybridization between the DDQ molecular level and nanotube valence bands transforms the semiconducting tube into a metallic one. Coupling of π electrons between tubes and aromatic molecules are observed. Our results show that noncovalent functionalization of carbon nanotubes by aromatic molecules is an efficient way to control the electronic properties of carbon nanotubes.

General Theory of Pseudopotentials

Abstract: It has previously been shown that the energy levels of valence electrons in atoms, molecules, and solids can be calculated from a weak net effective pseudopotential ${V}_{p}$. In ${V}_{p}$ most of the large negative potential energy of an electron, when inside the ion core of an atom, has been canceled against the large positive kinetic energy which the electron has there. It has recently been shown that there are several different forms which the pseudopotential can take. The theory is now developed from a different point of view, and it is shown that there exists an even wider class of pseudopotentials which all give the same valence energy levels. One of these, previously derived as an approximation, is now seen to be an exact form of the pseudopotential. Since it is much simpler and more convenient than other forms, its properties are investigated further with a view to its use for detailed numerical calculations. Finally, it is shown how the pseudopotential can be used not only for calculating valence energy levels, but also for the scattering of electrons by phonons and impurities in solids and by the disorder in liquid metals.

Unusual physical and chemical properties of Cu in Ce1-xCuxO2 oxides

Abstract: The structural and electronic properties of Ce1-xCuxO2 nano systems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Cu atoms embedded in ceria had an oxidation state higher than those of the cations in Cu2O or CuO. The lattice of the Ce1-xCuxO2 systems still adopted a fluorite-type structure, but it was highly distorted with multiple cation−oxygen distances with respect to the single cation−oxygen bond distance seen in pure ceria. The doping of CeO2 with copper introduced a large strain into the oxide lattice and favored the formation of O vacancies, leading to a Ce1-xCuxO2-y stoichiometry for our materials. Cu approached the planar geometry characteristic of Cu(II) oxides, but with a strongly perturbed local order. The chemical activities of the Ce1-xCuxO2 nanoparticles were tested using the reactions with H2 and O2 as probes. During the reduction in hydrogen...