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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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Journal ArticleDOI
TL;DR: A photoluminescence (PL) study of green-emitting SrGa2S4:Eu2+ phosphor is reported in this paper, where diffuse reflectance, excitation, and emission spectra are examined with the aim to enlarge the fundamental knowledge about the emission of the Eu 2+ ion in this lattice.

108 citations

Journal ArticleDOI
TL;DR: In this article, the authors extended the shell model for the very neutron-rich nuclei with $Zg~14$ to Al, Mg, Na, Ne, F, and O, using the same valence space and effective interaction.
Abstract: In this paper we extend the shell model calculations previously made for the very neutron-rich nuclei with $Zg~14$ to Al, Mg, Na, Ne, F, and O, using the same valence space and effective interaction. Predictions are made for the neutron separation energies and for the location of the neutron drip line. We find that the isotopes of Ne, Na, and Mg are deformed for $Ng~22.$ In ${}^{40}\mathrm{Mg},$ which is at the edge of the drip line, the $N=28$ shell closure does not stand. By enlarging the valence space to include intruder states we are able to account for the vanishing of the $N=20$ neutron shell closure in a small region around ${}^{31}\mathrm{Na}$ that we delineate. The dominance of the intruders explains the collective features experimentally found in this region.

108 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that the concentrations of structural defects and electronic gap states are quantitatively correlated, and that this way the electron deficiencies theoretically calculated for the valence bands of corresponding idealized structures are compensated.
Abstract: From fine-structure investigations it is well known that in many icosahedral boron-rich solids the occupation densities of specific atomic sites are considerably reduced. Investigations of the electronic properties have proved that the electronic properties of these semiconductors are strongly influenced by high densities of intrinsic states in the band gaps. For -rhombohedral boron and boron carbide, the best investigated icosahedral boron-rich solids, it is shown that the concentrations of structural defects and electronic gap states are quantitatively correlated, and that this way the electron deficiencies theoretically calculated for the valence bands of corresponding idealized structures are compensated. Obviously, the structural defects in these crystals are the necessary consequence of the valence electron deficiency. It is suggested that this correlation holds for the icosahedral boron-rich solids in general.

108 citations

Journal ArticleDOI
TL;DR: The results confirm the indication of Müller et al. (J Chem Phys 1999, 110, 7176) that the transition to the V state of ethene conforms to the Franck‐Condon principle and that it is not necessary to appeal to a nonvertical transition to interpret the experimental data.
Abstract: This article addresses an analysis of the physical effects required for the correct description of the ionic pi --> pi* excited states in the frame of ab initio quantum chemistry, using the ionic V state of the ethene molecule as an example. The importance of the dynamic sigma polarization (absent in methods where the sigma skeleton is treated at a mean-field level) has been recognized by many authors in the past. In this article a new physical effect is described, i.e. the spatial contraction of the pi and pi* molecular orbitals (or of the local p atomic orbitals) originated from the reduction of the ionicity due to the dynamic sigma polarization. Such an effect is a second-order effect (it appears only as a consequence of the dynamic sigma polarization) but it cannot be ignored. Many of the difficulties found in the past in the calculation of the vertical excitation energy of the ionic states are attributed to an incomplete description of this contraction, while the few successes have been obtained when it has been fortuitously introduced by ad hoc procedures or when it is described in a brute force approach. Various strategies are proposed to allow for the spatial contraction of the p atomic orbitals. If this effect is considered at the orbital optimization step, it is shown that for the V state of ethene no Rydberg/valence mixing occurs and a simple perturbation correction (to the second order in the energy) on the pi --> pi* singly excited configuration gives stable results with respect to the computational parameters and in good agreement with the experimental findings and with the best theoretical calculations. Moreover, our results confirm the indication of Muller et al. (J Chem Phys 1999, 110, 7176) that the transition to the V state of ethene conforms to the Franck-Condon principle and that it is not necessary to appeal to a nonvertical transition to interpret the experimental data. The strategy reported in this article for ethene can be in principle generalized to the pi --> pi* ionic excited states of other molecules.

108 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,521
20222,997
2021616
2020611
2019584
2018577