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51.
Marchand DJ De Filippis G Cataudella V Berciu M Nagaosa N Prokof'ev NV Mishchenko AS Stamp PC 《Physical review letters》2010,105(26):266605
We study a single polaron in the Su-Schrieffer-Heeger (SSH) model using four different techniques (three numerical and one analytical). Polarons show a smooth crossover from weak to strong coupling, as a function of the electron-phonon coupling strength λ, in all models where this coupling depends only on phonon momentum q. In the SSH model the coupling also depends on the electron momentum k; we find it has a sharp transition, at a critical coupling strength λ(c), between states with zero and nonzero momentum of the ground state. All other properties of the polaron are also singular at λ=λ(c). This result is representative of all polarons with coupling depending on k and q, and will have important experimental consequences (e.g., in angle-resolved photoemission spectroscopy and conductivity experiments). 相似文献
52.
Dominik Jacob Kathrin Thüring Aurellia Galliot Virginie Marchand Adeline Galvanin Akif Ciftci Karin Scharmann Michael Stock Jean‐Yves Roignant Sebastian A. Leidel Yuri Motorin Raffael Schaffrath Roland Klassen Mark Helm 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(28):9666-9670
53.
Simon G. Bott Alan P. Marchand Kaipenchery A. Kumar 《Journal of chemical crystallography》1996,26(4):281-286
Diels-Alder cycloaddition of cyclopentadiene (1a) to 2,3-dicyano-p-benzoquinone (2a), when performed in methanol solvent at ambient temperature, proceeds with kinetic control to afford 1,4,4a,8a-tetrahydro-5,8-dioxo-1,4-methanonaphthalene-4a,8a-dicarbonitrile (7, 77% yield). However, when this cycloaddition is performed by refluxing an equimolar solution of1a and2a in benzene for 3 h, the product of thermodynamic control, i.e., 1,4,4a,8a-tetrahydro-5,8-dioxo-1,4-methanonaphthalene-6,7-dicarbonitrile (3a) is obtained in 64% yield. The structure of3a was confirmed by an analysis of the reduced intramolecular photocyclization product,9. 相似文献
54.
Simon G. Bott Alan P. Marchand Kaipenchery A. Kumar D. Vidyanand Dongxia Xing William H. Watson Ram P. Kashyap Richard A. Sachleben 《Journal of chemical crystallography》1995,25(10):633-640
The crystal structures of three compounds formedvia nucleophilic attack of a heterocyclic secondary amine on PCU-8,11-dione, with the concomitant intramolecular attack of one keto oxygen on the carbon of the other ketone, are presented. In all three compounds, the bridging oxygen contains substantial p-character, and the bonds to the attacking nitrogen are significantly shorter than would be expected. 相似文献
55.
Andrew Burritt Mariusz Krawiec Alan P. Marchand Duoli Sun William H. Watson 《Journal of chemical crystallography》1995,25(2):63-68
In the solid state the 21 Diels-Alder adduct between spiro[4.2]hepta-1,3-diene and p-benzoquinone has a planar cyclohexadione ring with a center of symmetry. Both planar and boat conformations have been observed in similar systems, and the relative stability of the two conformers is of interest. The adduct in the gas phase should contain a mirror plane perpendicular to the cyclohexadione ring; however, a data set collected on a crystal in a capillary resulted in a structure where some bond lengths related by this mirror plane differed by more than 4 in the solid state. Molecular mechanics, MOPAC, and the Cambridge Structural Data Base were used to investigate the factors influencing the conformation of the cyclohexadione ring and the asymmetry across the noncrystallographic mirror plane. The energy differences between the planar and nonplanar ring system is small, and the conformation is determined by crystal packing. No reason for the bond length asymmetry could be found, and a recollection of data on a crystal exposed to the environment led to a structure with statistically equivalent bond lengths. 相似文献
56.
57.
A. Alan Pinkerton Pannee M. Burckel Alan P. Marchand Eric Zhiming Dong 《Journal of chemical crystallography》1998,28(12):913-917
The X-ray crystal structure of the title compound is reported. Crystal data: T = 100 K, monoclinic, P21/n, a = 8.2990(17), b = 13.2300(26), c = 12.0350(24) Å, = 93.676(30)°, V = 1318.7 (5) Å3, and R = 0.0368. The methylene carbon atoms in the cyclohexadiene ring are disordered over two positions above and below the ring plane. The chlorine substituted endocyclic double bond deviates from planarity with an angle of 8.10(13)° toward the endo-face. The facially differentiated 1,3-cyclohexadiene moiety is only slightly pyramidalized, deviating 1.75(20)° also toward the endo-face of the tricyclic system. 相似文献
58.
Ram P. Kashyap Mahendra N. Deshpande Dayanada Rajapaksa Alan P. Marchand William H. Watson 《Journal of chemical crystallography》1995,25(9):573-578
Hexacyclo[6.5.0.02,7.04,12.05,10.09.13]tridecane (HCTD) contains two four-membered, two five-membered and two six-membered rings fused into a cage structure which contains about 77.0 kcal/mol of strain energy. Attempts to prepare the thioketal from the diketone of HCTD led to a skeletal rearrangement to produce a cage with one four-membered, four five-membered, and two six-membered rings fused into a cage (RHCTD). The corresponding RHCTD hydrocarbon has a strain energy 13.7 kcal/mol less than that of the starting tridecane (HCTD) which provides the driving force for the rearrangement. The X-ray structures of two HCTD derivatives and one RHCTD derivative are reported. The bond lengths in the three reported structures are normal for cages of this type. The structure of tetracyclo[6.3.0.03,7.04,11]undecane-5,10-dione mono(ketene 1,3-propanedithioacetal) is discussed also. 相似文献
59.
The structure of a bis(benzyloxy)trishomocubanone with molecular C2 symmetry reveals that substitution of benzyloxy groups has little effect on the trishomocubane cage. 相似文献
60.
Simon G. Bott Alan P. Marchand Duddu Raja Gopal 《Journal of chemical crystallography》1993,23(11):849-855
The syntheses and crystal structures of pentacyclo[9.4.1.05,14.07,13.012,15]hexadecane-3,9-dione (2), a novel C16 diketone with potential inclusion ability, and the products of the reaction of2 withn-butyllithium andmeso-erythritol (i.e.,meso-1,2,3,4-butanetetrol) are described. Crystal data:2·H2O, orthorhombic,Pmmn,a=10.7385(8),b=9.0188(6),c=6.8411(4)Å,V=662.55(7)Å3, andR=0.039 (379 reflections);3 (product from reaction withn-butyllithium), triclinic,P¯1,a=8.7192(7),b=10.9351(8),c=12.1842(8)Å,=68.933(5),=75.850(6), =80.309(6)°,V=1047.0(1)Å3, andR=0.081 (1811 reflections);4 (product from reaction with erythritol), triclinic,P¯1,a=7.7224(8),b=10.1976(8),c=10.7021(9)Å,=85.405(7),=85.766(8), =76.056(7)°,V=814.0(1)Å3, andR=0.052 (1471 reflections). 相似文献