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.

Electron-electron interaction and localization in d and f transition metals

Abstract: We discuss, for the d and f transition metals, the competition between atomiclike electrostatic Coulomb and exchange interactions and loss of atomic characteristics in the solid through screening of f and d charge fluctuations and hybridization. We derive semiempirical relations describing these interactions for the 3d, 4d, 5d, 4f, and 5f elements in the environment of a metallic host. We then compare these to the hybridization widths, also semiempirically determined, and arrive at conclusions concerning the localization of the d or f electrons and the formation of magnetic moments. We show that some of the light actinides can exhibit negative ${U}^{\mathrm{eff}}$ behavior dependent on their valence in the solid. We argue that some d transition metals may belong to the same group if properly alloyed.

Conductive lithium storage electrode

Abstract: A compound comprising a composition A.(M'1-aM"a)y(XD4)z, .ALPHA.,(M'1-aM"a)y(DXD4)z, or Ax,(M'1-aM''a)y(X2D7)z, and have values such that x, plus y(l -a) times a formal valence or valences of M', plus ya times a formal valence or valence of M", is equal to z times a formal valence of the XD4, X2D7, or DXD4 group; or a compound comprising a composition (A1-aM"a)xM'y(XD4)z, (A1-aM"a)xM'y(DXD4)z (A1-aM"a)xM'y(X2D7)z and have values such that (1-a)x plus the quantity ax times the formal valence or valences of M" plus y times the formal valence or valences of M' is equal to z times the formal valence of the XD4, X2D7 or DXD4 group. In the compound, A is at least one of an alkali metal and hydrogen, M' is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, molybdenum, and tungsten, M" any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen, carbon, or a halogen, 0.0001 < a <= 0.1, and x, y, and z are greater than zero. The compound can have a conductivity at 27~ C of at least about 10-8 S/cm. The compound can be a doped lithium phosphate that can intercalate lithium or hydrogen. The compound can be used in an electrochemical device including electrodes and storage batteries and can have a gravimetric capacity of at least about 80 mAh/g while being charged/discharged at greater than about C rate of the compound.

Molecular core-valence correlation effects involving the post-d elements Ga-Rn: benchmarks and new pseudopotential-based correlation consistent basis sets.

Abstract: Correlation consistent basis sets that are suitable for the correlation of the outer-core (n−1)spd electrons of the post-d elements Ga–Rn have been developed. These new sets, denoted by cc-pwCVXZ-PP (X=D,T,Q,5), are based on the previously reported cc-pVXZ-PP sets that were built in conjunction with accurate small-core relativistic pseudopotentials (PPs) and designed only for valence nsp correlation. These new basis sets have been utilized in benchmark coupled cluster calculations of the core-valence correlation effects on the dissociation energies and spectroscopic properties of several small molecules. As expected, the most important contribution is the correlation of the (n−1)d electrons. For example, in the case of the group 13 homonuclear diatomics (Ga2,In2,Tl2), this leads to a dissociation energy increase compared to a valence-only treatment from 1.5 to 3.2 kcal/mol, bond length shortenings from −0.076 to −0.125 A, and harmonic frequency increases of 7–8 cm−1. Even in the group 15 cases (As2,Sb2,Bi2), the analogous effects of (n−1)d electron correlation are certainly not insignificant, the largest values being +4.4 kcal/mol, −0.049 A, and +9.6 cm−1 for the effects on De, re, and ωe, respectively. In general, the effects increase in magnitude down a group from 4p to 6p. Correlation of the outer-core (n−1)p electrons is about an order of magnitude less important than (n−1)d but larger than that of the (n−1)s. The effect of additional tight functions for Hartree–Fock and valence sp correlation was found to be surprisingly large, especially for the post-4d and post-5d elements. The pseudopotential results for the molecules containing post-3d elements are also compared to the analogous all-electron calculations employing the Douglas–Kroll–Hess Hamiltonian. The errors attributed to the PP approximation are found to be very small.

On the interpretation of molecular valence Auger spectra

Abstract: The interpretation of molecular valence Auger spectra by means of ab initio computational methods is discussed. As alternatives to self‐consistent‐field optimizations of the full Auger spectrum, the feasibility of a procedure based on single ionization potentials and of CI calculations using frozen orbitals is tested. Numerical calculations are performed for the CO, N2, NO, and CO2 molecules, which show especially structure‐rich Auger spectra. These spectra are analyzed in detail and they are found to contain three nonoverlapping regions of transitions corresponding to final state vacancies in outer–outer, outer–inner, and inner–inner valence orbitals. It is investigated whether this division of the transitions also is relevant with respect to the magnitude of dynamical relaxation errors in the single ionization potential procedure or with respect to the choice of molecular orbital basis in the CI calculations. CI effects are found to be important for intensities and energies of the Auger transitions in t...