Topic
Multiplicity (chemistry)
About: Multiplicity (chemistry) is a research topic. Over the lifetime, 1476 publications have been published within this topic receiving 25036 citations. The topic is also known as: degeneracy & statistical weight.
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TL;DR: In this article, the absorption spectra of metal porphyrins derived from the basic skeleton are discussed in terms of a four-orbit model, that is intensity changes and energy shifts are related to the properties of two top filled and two lowest empty pi orbitals.
1,866 citations
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TL;DR: In this article, it was shown that the energy splitting depends linearly on the coefficient of exact exchange admixture, and that Becke's 20% admixture should be reduced to about 15% if meaningful energetics are sought for transition-metal compounds.
Abstract: Low-spin/high-spin energy splittings for Fe(II) transition-metal complexes – particularly in weak ligand fields – cannot be well described by density functional methods. Different density functionals yield results which differ by up to 1 eV in transition-metal complexes with sulfur-rich first coordination spheres. We attribute this failure to the fact that the high-spin state is systematically favoured in Hartree–Fock-type theories, because Fermi correlation is included in the exact exchange, while Coulomb correlation is not. We thus expect that the admixture of exact exchange to a given density functional will heavily influence the energy splitting between states of different multiplicity. We demonstrate that the energy splitting depends linearly on the coefficient of exact exchange admixture. This remarkable result is found for all the Fe(II)–S complexes studied. From this observation we conclude in connection with experimental results that Becke's 20% admixture should be reduced to about 15% if meaningful energetics are sought for transition-metal compounds. We rationalize that this reduction by 5% will not affect the quality of the hybrid functional since we arrive at a slightly modified functional, which lies between the pure density functional and the hybrid density functional, which both give good results for “standard” systems.
1,188 citations
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TL;DR: In this paper, the multiplicity and the full spin of the ground state of large alternate molecules with conjugated bonds are considered and it is strictly shown that if the numbers of starred and unstarred atoms (say, carbon) differ from each other, the full-spin of the molecule is more than zero.
Abstract: The multiplicity and the full spin of the ground state of large alternate molecules with conjugated bonds are considered. It is strictly shown that if the numbers of starred and unstarred atoms (say, carbon) differ from each other the full spin of the molecule is more than zero. Some possible planar and linear molecules having the full spin to be proportional to their sizes are presented. Particularly, they would be ferromagnets at infinite sizes.
675 citations
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367 citations
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TL;DR: In this article, the first direct measurements of charged particle multiplicity distributions for pp collisions at ISR energies were performed by means of a streamer chamber detector with large solid-angle coverage and excellent multitrack efficiency.
326 citations