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51.
To provide theoretical insight into the structures and properties of Sc3N@C80, which has been isolated in high yield and purity as a new stable endohedral metallofullerene, density functional calculations are carried out for the Sc3?nLanN@C80 (n=0–3) series. Because of electron transfer from Sc3N to C80, the electronic structure of Sc3N@C80 is formally described as (Sc3N)6+C$_{80}^{6-}$. The encapsulated Sc3N cluster takes a planar structure with long Sc–Sc distances and is highly stabilized inside the Ih cage of C80, which rotates rapidly. As the number of La atoms increases, the Sc3?nLanN cluster is forced to maintain a pyramidal structure in Sc3?nLanN@C80. In addition, the C80 cage takes an open‐shell electronic structure due to an increase in the number of electrons transferring from Sc3?nLanN. These make the endohedral structure less stable and more reactive. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1353–1358, 2001 相似文献
52.
Marcel Erné 《Algebra Universalis》1994,31(1):36-65
Although the categoryCLC of complete lattices and complete homomorphisms does not possess arbitrary coproducts, we show that the tensor product introduced by Wille has the universal property of coproducts for so-called distributing families of morphisms (and only for these). As every family of morphisms into a completely distributive lattice is distributing, this includes the known fact that in the category of completely distributive lattices, arbitrary coproducts exist and coincide with the tensor products. Since the definition of tensor products is based on the notion of contexts and their concept lattices, many results on tensor products extend from complete lattices to contexts. Thus we introduce two kinds of tensor products for arbitrary families of contexts, a partial and a complete one, and establish universal properties of these tensor products.Presented by B. Jonsson. 相似文献
53.
Uwe Grimm 《Letters in Mathematical Physics》1994,32(3):183-187
Explicit expressions for three series ofR matrices which are related to a dilute generalisation of the Birman-Wenzl-Murakami algebra are presented. Of those, one series is equivalent to the quantumR matrices of theD
n+1
(2)
generalised Toda systems, whereas the remaining two series appear to be new. 相似文献
54.
Ezer Melzer 《Letters in Mathematical Physics》1994,31(3):233-246
We prove an identity between three infinite families of polynomials which are defined in terms of bosonic, fermionic, and one-dimensional configuration sums. In the limit where the polynomials become infinite series, they give different-looking expressions for the characters of the two integrable representations of the affine su(2) algebra at level one. We conjecture yet another fermionic sum representation for the polynomials which is constructed directly from the Bethe-ansatz solution of the Heisenberg spin chain. 相似文献
55.
Two Fraenkel-Mostowski models are constructed in which the Boolean Prime Ideal Theorem is true. In both models, AC for countable sets is true, but AC for sets of cardinality 2 and the 2m = m principle are both false. The Principle of Dependent Choices is true in the first model, but false in the second. Mathematics Subject Classification: 03E25, 03E35, 04A25. 相似文献
56.
We consider a class of vertex models describing directed lines on a lattice in arbitraryd dimensions, and solve the model exactly for the Cartesian lattice and in the case that each loop of lines carries a fugacity - 1. Our analysis, which can be carried out for arbitrary lattices, is based on an equivalence of the vertex model with a dimer problem. The dimer problem is, in turn, solved using the method of Pfaffians. It is found that the system is frozen below a critical temperatureT
cwith the critical exponent = (3 –d)/2. 相似文献
57.
Reinhard Honegger 《Letters in Mathematical Physics》1993,27(3):191-203
By means of cocycle techniques in a recent paper, the global dynamics of mean field-boson couplings has been studied. Here, by restricting to the bosonic system the infinite time limit (t ) for very general initial states, one obtains time-asymptotic states on the bosonicC
*-Weyl algebra, in which one partially rediscovers the collective ordering of the infinite mean field lattice. 相似文献
58.
59.
In this B3 LYP model study, homoleptic nickel(0) ethyne complexes have been predicted as the catalyst resting state for the title reaction. Ethyne ligand coupling of Ni(C(2)H(2))(3) yields monoethyne nickelacyclopentadiene in the rate-determining step. Ethyne coordination is followed by insertion of an ethyne ligand into the Ni--C sigma bond. A highly strained monoethyne trans-nickelacycloheptatriene is formed. This trans intermediate is unable to reductively eliminate benzene without prior isomerization to a cis-structure. Instead, it rapidly collapses to a nickelacyclononatetraene. Ethyne coordination induces reductive elimination to the cyclooctatetraene complex Ni(eta(2)-C(2)H(2))(eta(2)-C(8)H(8)), followed by facile ligand exchange. Other ethyne coupling pathways have been computed to be less favored. The cyclooctatetraene ligand binds significantly weaker to nickel(0) than ethyne, both for mononuclear, and for dinuclear species. For this reason, C--C bond formation steps at Ni(2)(micro-cot) fragments have been predicted to feature prohibitively high overall reaction barriers. 相似文献
60.
Marcel Erné 《Order》1985,2(2):199-210
A standard extension for a poset P is a system Q of lower ends (descending subsets) of P containing all principal ideals of P. An isomorphism between P and Q is called recycling if [Y]Q for all YQ. The existence of such an isomorphism has rather restrictive consequences for the system Q in question. For example, if Q contains all lower ends generated by chains then a recycling isomorphism between P and Q forces Q to be precisely the system of all principal ideals. For certain standard extensions Q, it turns out that every isomorphism between P and Q (if there is any) must be recycling. Our results include the well-known fact that a poset cannot be isomorphic to the system of all lower ends, as well as the fact that a poset is isomorphic to the system of all ideals (i.e., directed lower ends) only if every ideal is principal. 相似文献