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.

A theoretical study of the valence‐ and dipole‐bound states of the nitromethane anion

Abstract: The valence‐ and dipole‐bound states of CH3NO−2 are studied at the CCSD(T), HFDFT (B3LYP), and EA‐EOMCC levels of theory. At both CCSD(T) and HFDFT levels, we have found a positive valence EA in nice agreement with the experimental data. The binding energy of the dipole‐bound electron is about 13 meV according to the EA‐EOMCC calculations. Interaction of the valence‐ and dipole‐bound states (DBS) of CH3NO−2 is complicated, since the dipole‐bound state exists at the equilibrium geometry of the anion and corresponds to an excited state of the valence‐bound anion. Hence, excitations of the valence anionic state could lead to both the detachment of an electron or formation of a DBS, whose geometry is similar to the geometry of the neutral parent. At the equilibrium geometry of the anion, the energies of the dipole‐bound and valence states are close to each other. Since typical lifetimes of rovibrational excited states of a DBS are two orders of magnitude higher than the lifetimes of ordinary vibrationally exc...

Differences between L3 and L2 x‐ray absorption spectra of transition metal compounds

Abstract: The differences between L3 and L2 edges of 3d and 4d transition metal complexes and compounds in octahedral symmetry are discussed. The main origin of these differences are the multiplet effects due to the coupling of the 2p core wave function and the 3d and 4d valence wave functions. The 3d and 4d spin–orbit coupling is a second origin of difference. For 3d systems the multiplet effects dominate all other interactions and the L3 and L2 edge are completely mixed and reordered. For 4d systems the core hole spin–orbit coupling is large and the L3 and L2 are separated by about 100 eV with a ratio close to 2:1. The differences between the L3 and L2 edge originate from the weight transfer between the t2g and eg peaks due to the multiplet effect. This weight transfer is about 25% for the L3 edge and about 5% for the L2 edge, which implies that for a comparison to single‐particle calculations the L2 edge is preferable to use. Partly filled 4d systems are low‐spin and the occupation of the t2g states implies a de...

A local Fermi liquid theory of intermediate valence systems

Abstract: A non-interacting local Fermi liquid theory applicable to Ce, Sm, Eu and Yb metallic intermediate valence materials is presented. The induced density of states of a given rare earth ion is taken as the Lorentzian appropriate for a rare earth ion impurity, for which the justification is tentatively discussed. The degeneracy of the resonance is that of the magnetic configuration of the ion. The results are applied to the f occupation, susceptibility and specific heat. A relationship existing in the literature between the zero temperature susceptibility and linear coefficient of specific heat follows exactly from the present very simple theory. The results are compared with a range of experimental data.

Anomalous bulk photovoltaic effect in ferroelectrics: A quadratic response theory

Abstract: We present a phenomenological description and a quantum-mechanical theory of electron transport in the anomalous bulk photovoltaic effect (ABPVE) in ferroelectrics. Our theory is based on a quadratic response formalism which leads to an exact expression for the short-circuit photovoltaic current (SCPVC). This theory indicates the existence of an ABPVE even in a system of pure Bloch states. We demonstrate the capability of our theory by performing an explicit calculation of the SCPVC for a one-dimensional model of independent impurities. From these results we conclude that sign changes of the SCPVC, as observed in BaTi${\mathrm{O}}_{3}$, are either due to impurities which have a bound excited state, or to Bloch states with two or more overlapping valence or conduction bands. There is evidence for both mechanisms.