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排序方式: 共有59条查询结果,搜索用时 328 毫秒
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Eva-Maria Niehaus Karin Kleigrewe Philipp Wiemann Lena Studt Christian M.K. Sieber Lanelle R. Connolly Michael Freitag Ulrich Güldener Bettina Tudzynski Hans-Ulrich Humpf 《Chemistry & biology》2013,20(8):1055-1066
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4.
Wanko M Garavelli M Bernardi F Niehaus TA Frauenheim T Elstner M 《The Journal of chemical physics》2004,120(4):1674-1692
This work investigates the capability of time-dependent density functional response theory to describe excited state potential energy surfaces of conjugated organic molecules. Applications to linear polyenes, aromatic systems, and the protonated Schiff base of retinal demonstrate the scope of currently used exchange-correlation functionals as local, adiabatic approximations to time-dependent Kohn-Sham theory. The results are compared to experimental and ab initio data of various kinds to attain a critical analysis of common problems concerning charge transfer and long range (nondynamic) correlation effects. This analysis goes beyond a local investigation of electronic properties and incorporates a global view of the excited state potential energy surfaces. 相似文献
5.
H.C. Mastwijk M. van Rijnbach J.W. Thomsen P. van der Straten A. Niehaus 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(2):131-137
This paper presents an experimental investigation of cold collisions between metastable helium atoms in an optical trap at
1 mK. Penning (PI) and associative (AI) ionization reactions are distinguished using a mass spectrometer and studied under
influence of near resonant laser light. Dramatic enhancement, by more than a factor 15, of the ion rate is observed when the
laser is tuned close to resonance. Experimental findings are well-described, on an absolute scale, by model predictions.
Received: 9 February 1998 / Revised: 4 May 1998 / Accepted: 14 May 1998 相似文献
6.
C. J. Zwakhals R. Morgenstern A. Niehaus 《Zeitschrift für Physik A Hadrons and Nuclei》1982,307(1):41-49
We present electron energy spectra that arise in Li+ —He collisions in the laboratory collision energy range from 1.4 to 3 keV, and that are observed at 0° and 180° with respect to the Li+ beam. The spectra are composed of a component due to atomic autoionization of doubly excited He in the field of Li+, and a component due to molecular autoionization of the collision system. The variation of the latter component with collision energy and observation angle is analyzed in terms of a newly developed spectral shape function for molecular autoionization that implies a “distribution of travelling velocities” of the collision system during electron emission. From the comparison of calculated and measured spectra it is concluded that the physical interpretation on which the analysis is based is correct. Two parameters of the distribution of travelling velocities are determined. 相似文献
7.
Lin CS Zhang RQ Lee CS Niehaus TA Frauenheim T 《The journal of physical chemistry. B》2006,110(42):20847-20851
The energetics and luminescent property of a guest molecule, 1,4-bis(benzothiazolylvinyl)benzene (BT), interacting with a host molecule, 2,2',2' '-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI), in organic light-emitting diodes are studied by performing excited-state calculations using a time-dependent density-functional tight-binding method complemented with dispersion energy. It is found that the overlap between the TPBI emission and the BT absorption spectra shows an efficient energy transfer from the host molecule to the guest molecule when they are excited. The planar BT molecule becomes distorted when it is mixed with TPBI, resulting in a blue luminescence around 475 nm. The separation of the TPBI + BT mixture on a graphite surface is found to be energetically favorable, consistent with experimental observation. 相似文献
8.
Biocatalytic deuterium- and hydrogen-transfer using over-expressed ADH-'A': enhanced stereoselectivity and 2H-labeled chiral alcohols 总被引:1,自引:0,他引:1
Edegger K Gruber CC Poessl TM Wallner SR Lavandera I Faber K Niehaus F Eck J Oehrlein R Hafner A Kroutil W 《Chemical communications (Cambridge, England)》2006,(22):2402-2404
Employing the over-expressed highly organic solvent tolerant alcohol dehydrogenase ADH-'A' from Rhodococcus ruber DSM 44541, versatile building blocks, which were not accessible by the wild type catalyst, were obtained in > 99% e.e.; furthermore, employing d8-2-propanol as deuterium source, stereoselective biocatalytic deuterium transfer was made feasible to furnish enantiopure deuterium labeled sec-alcohols on a preparative scale employing a single enzyme. 相似文献
9.
Heringer D Niehaus TA Wanko M Frauenheim T 《Journal of computational chemistry》2007,28(16):2589-2601
An analytical formulation for the geometrical derivatives of excitation energies within the time-dependent density-functional tight-binding (TD-DFTB) method is presented. The derivation is based on the auxiliary functional approach proposed in [Furche and Ahlrichs, J Chem Phys 2002, 117, 7433]. To validate the quality of the potential energy surfaces provided by the method, adiabatic excitation energies, excited state geometries, and harmonic vibrational frequencies were calculated for a test set of molecules in excited states of different symmetry and multiplicity. According to the results, the TD-DFTB scheme surpasses the performance of configuration interaction singles and the random phase approximation but has a lower quality than ab initio time-dependent density-functional theory. As a consequence of the special form of the approximations made in TD-DFTB, the scaling exponent of the method can be reduced to three, similar to the ground state. The low scaling prefactor and the satisfactory accuracy of the method makes TD-DFTB especially suitable for molecular dynamics simulations of dozens of atoms as well as for the computation of luminescence spectra of systems containing hundreds of atoms. 相似文献
10.
Optimized Crossover-Based Genetic Algorithms for the Maximum Cardinality and Maximum Weight Clique Problems 总被引:1,自引:0,他引:1
In Balas and Niehaus (1996), we have developed a heuristic for generating large cliques in an arbitrary graph, by repeatedly taking two cliques and finding a maximum clique in the subgraph induced by the union of their vertex sets, an operation executable in polynomial time through bipartite matching in the complement of the subgraph. Aggarwal, Orlin and Tai (1997) recognized that the latter operation can be embedded into the framework of a genetic algorithm as an optimized crossover operation. Inspired by their approach, we examine variations of each element of the genetic algorithm—selection, population replacement and mutation—and develop a steady-state genetic algorithm that performs better than its competitors on most problems. 相似文献