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171.
Recent calculations on the formation of self-trapped amide group vibrational states in alpha-helical polypeptides [J. Chem. Phys. 124, 134907 (2006)] are extended to the amide N-H normal mode vibrations. First, the adiabatic N-H vibrational single- and two-exciton states are examined by treating the longitudinal chain coordinates as parameters. Then, in using the multiconfiguration time-dependent Hartree method coupled exciton-chain vibrational quantum dynamics are accounted for. Based on the respective exciton-chain vibrational wave function propagation the infrared transient absorption related to a sequential pump-probe experiment is calculated. The modulation of local amide vibrational energies by the longitudinal chain coordinates is found to have a pronounced effect on the broadening of absorption lines. Moreover, the ultrafast exciton transfer in the system is studied in order to characterize the dynamics of the self-trapped single-exciton states on a time scale below 10 ps. 相似文献
172.
The recently introduced MP2-R122*A(loc) and LMP2-R122*A(loc) methods are modified to use a short-range correlation factor expanded as a fixed linear combination of Gaussian geminals. Density fitting is used to reduce the effort for integral evaluation, and local approximations are introduced to improve the scaling of the computational resources with molecular size. The MP2-F122*A(loc) correlation energies converge very rapidly with respect to the atomic orbital basis set size. Already with the aug-cc-pVTZ basis the correlation energies computed for a set of 21 small molecules are found to be within 0.5% of the MP2 basis set limit. Furthermore the short-range correlation factor leads to an improved convergence of the resolution of the identity, and eliminates problems with long-range errors in density fitting caused by the linear r12 factor. The DF-LMP2-F122*A(loc) method is applied to compute second-order correlation energies for molecules with up to 49 atoms and more than 1600 basis functions. 相似文献
173.
May Nyman Todd M. Alam François Bonhomme Mark A. Rodriguez Colleen S. Frazer Margaret E. Welk 《Journal of Cluster Science》2006,17(2):197-219
The hexaniobate Lindqvist ion
has long been known as the dominant specie in alkaline niobium oxide solutions. Recent advances in heteropolyniobate chemistry continue to be greatly aided by use of
alkali salts as soluble precursors; in particular, potassium, sodium and lithium hexaniobate salts. We report here the solid-state characterization and solution behavior of Li, K, Rb and Cs Lindqvist
salts. Synthesis and single-crystal X-ray diffraction data is reported for nine new hexaniobate salts. These structures differ in the number of charge-balancing alkali cations, protonation of the clusters, relative arrangement of the clusters and alkali metal cations, amount of lattice water and its mode of interaction with other lattice species. Trends of alkali-cluster bonding are observed as a function of alkali radius. Protonation of the clusters in the solid-state is influenced by the method of crystallization of the
salt. Lability of the cluster oxygens is observed by solution 17O NMR experiments. Rates of isotopic enrichment of the bridging oxygen, terminal oxygen and bridging hydroxyl cluster sites are compared for aqueous solutions of Li, K, Rb and Cs hexaniobate salts. Parameters influencing the oxo-ligand exchange rates of the salts are discussed relative to their use as heteropolyniobate precursors.This paper is dedicated to Professor Michael T. Pope on the event of his retirement to acknowledge his fruitful career in polyoxometalate chemistry. 相似文献
174.
By means of molecular dynamics simulations we investigate the Stokes–Einstein behaviour of the Gaussian Core Model liquid at high densities. From a recent analysis at moderately high densities, we found that the Stokes–Einstein factor grows linearly with the viscosity. We show that at high densities the behaviour is similar, but there are slight departures at lower temperatures and higher densities. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
175.
M.A. Barrios K.B. Fournier S.P. Regan O. Landen M. May Y.P. Opachich K. Widmann D.K. Bradley G.W. Collins 《High Energy Density Physics》2013,9(3):626-634
K-shell X-ray emission from laser-irradiated planar Zn, Ge, Br, and Zr foils was measured at the National Ignition Facility for laser irradiances in the range of 0.6–9.5 × 1015 W/cm2. The incident laser power had a pre-pulse to enhance the laser-to-X-ray conversion efficiency (CE) of a 2–5 ns constant-intensity pulse used as the main laser drive. The measured CE into the 8–16 keV energy band ranged from 0.43% to 2%, while the measured CE into the He-like resonance 1s2–1s2p(1P) and intercombination 1s2–1s2p(3P) transitions, as well as from their 1s2(2s,2p)l–1s2p(2s,2p)l satellite transitions for l = 1, 2, 3, corresponding to the Li-, Be-, and B-like resonances, respectively, ranged from 0.3% to 1.5%. Absolute and relative CE measurements are consistent with X-ray energy scaling of (hν)?3 to (hν)?5, where hν is the X-ray energy. The temporal evolution of the broadband X-ray power was similar to the main laser drive for ablation plasmas having a critical density surface. 相似文献
176.
177.
The asymmetric hydrogenation of tetrasubstituted α,β-unsaturated ketones has been accomplished using an in situ formed rhodium-Josiphos catalyst. The reaction is enhanced by addition of catalytic zinc(II) triflate, which significantly improves turnover frequency while suppressing epimerization of the products. 相似文献
178.
Gil A Karhánek D Miró P Antonio MR Nyman M Bo C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(27):8340-8346
Anionic uranyl-peroxide U(28) nanocapsules trap cations and other anions inside, whose structures cannot be resolved by X-ray diffraction, owing to crystallographic disorder. DFT calculations enabled the complete characterization of the geometry of these complex systems and also explained the origin of the disorder. The stability of the capsules was strongly influenced by the entrapped cations. Excellent agreement between experiment and theory was also obtained for the electronic character and redox properties. 相似文献
179.
T Sainsbury A Satti P May A O'Neill V Nicolosi YK Gun'ko JN Coleman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(35):10808-10812
The covalent functionalization of exfoliated hexagonal boron nitride (h-BN) nanosheets by nitrene addition is described. Integration of functionalized h-BN nanosheets within a polycarbonate matrix is demonstrated and was found to afford significant increases in mechanical properties. This integration methodology was further extended by the covalent modification of the h-BN nanosheets with polymer chains of a polycarbonate analogue, and the integration of the polymer modified h-BN within the polymer matrix. 相似文献
180.
A. Schmidt F. Garwe U. Hübner T. May W. Paa M. Zeisberger G. Zieger H. Stafast 《Applied physics. B, Lasers and optics》2012,109(4):631-642
The THz radiation emission of Au-coated nanogratings (fused silica substrate, 30?nm Au layer thickness, 500?nm grating constant) upon fs laser irradiation (785?nm, 150?fs, 1?kHz,???1?mJ/pulse) is observed in both directions along the laser beam axis (forward and backward) and for both, illumination of the Au/air or the Au/silica interface. THz radiation along the laser beam propagation is emitted in a narrow solid angle of about 15°?fwhm independent on the laser pulse fluence, the angle of incidence and the nanograting profile. The bar width and groove depth of the nanograting as well as the angle of laser beam incidence strongly affect the THz radiation yield. The energy of single THz light pulses is measured absolutely (2?fJ in the 0.3?C0.38?THz range) using a highly sensitive and fast superconducting transition edge sensor. The bi-directional emission of THz radiation is in agreement with the model assumption of surface plasmon polaritons propagating simultaneously on both Au layer interfaces (Au/air and Au/silica). 相似文献