Topic
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.
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TL;DR: The magnetic susceptibility, electrical resistivity, Hall effect, NMR, XPS and specific heat measurements indicate that YbB12 is a mixed valence compound with the valence of + 2.9, and as the temperature decreases χ goes through a peak at 75 K and then decreases rapidly to a constant value after subtraction of impurity effect as discussed by the authors.
116 citations
TL;DR: In this paper, it was shown that the sensitivity of the transverse-acoustic modes to covalent bonding is related to the magnitude of the effect from zero to the melting temperature.
Abstract: The direct and indirect gaps between valence and conduction bands in semiconductors usually decrease with temperature. This effect is related by thermodynamic identities to the influence of electron-hole pairs on the lattice vibration frequencies. We show that the surprisingly large magnitude of the effect in Si and similar semiconductors is related to the sensitivity of the transverse-acoustic modes to covalent bonding. We are able to account for the magnitude of the effect from zero to the melting temperature. We also account for anomalous temperature variation in HgTe and related cases and mention other applications of the theory.
116 citations
TL;DR: In this article, the geometry and vibrational frequencies of the water dimer were calculated using ab initio LCAO-SCF theory using a split valence basis set.
116 citations
15 Aug 2002
TL;DR: In this article, the concept of overlap polarizability of a single directional chemical bond is introduced and an expression for this quantity is proposed, as a consequence of a relation involving the bond force constant and the square of the overlap charge.
Abstract: We introduce the concept of overlap polarizability of a single directional chemical bond and propose an expression for this quantity. The concept of ionic specific valence is also introduced, as a consequence of a relation, involving the bond force constant, between the overlap polarizability and the square of the overlap charge. It is proposed that the overlap polarizability can be used to define an ordinal scale of covalency. When applied to lanthanide compounds, each pair lanthanide-ligating atom being regarded as a diatomic-like molecule, these concepts lead to a remarkable result in which an expression for the charge factors, appearing in the simple overlap model for the ligand field, can be obtained when these factors are identified with the ionic specific valences of the ligating atoms. An ordinal scale of covalency for a few representative lanthanide compounds correlates well with the nephelauxetic effect.
116 citations
TL;DR: In this paper, the Green's function decoupling methods of the Hubbard Hamiltonian were used to show that intersite correlations profoundly affect states near the Fermi energy and may lead to a small insulating gap if the two bands contain an even integral number of electrons per rare earth ion.
Abstract: Mixed valence systems exhibit an interesting variety of low temperature electronic phenomena, in particular, a remarkable division of the known mixed valence compounds into metallic and insulating groups, exemplified respectively by CePd3 and SmB6. We show that for Sm compounds it is appropriate to use a two‐band Hubbard Hamiltonian comprised of a narrow f band with a large Coulomb interaction U, a wide d band with negligible interactions, and f‐d hybridization, Coulomb, and exchange interactions. Using the Green’s function decoupling methods of Hubbard, we show that intersite correlations profoundly affect states near the Fermi energy and may lead to a small insulating gap if the two bands contain an even integral number of electrons per rare earth ion, as in stoichiometric SmB6. Magnetic phase transitions are discussed in terms of exchange vs. hybridization energies, and a first order transition from a paramagnetic insulator to a ferro‐ or ferrimagnetic metal is predicted within the mixed valence regime.
116 citations