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221.
Kjaergaard T Jørgensen P Olsen J Coriani S Helgaker T 《The Journal of chemical physics》2008,129(5):054106
We present a second-quantization based atomic-orbital method for the computation of time-dependent response functions within Hartree-Fock and Kohn-Sham density-functional theories. The method is suited for linear scaling. Illustrative results are presented for excitation energies, one- and two-photon transition moments, polarizabilities, and hyperpolarizabilities for hexagonal BN sheets with up to 180 atoms. 相似文献
222.
Høst S Jansík B Olsen J Jørgensen P Reine S Helgaker T 《Physical chemistry chemical physics : PCCP》2008,10(35):5344-5348
Kohn-Sham density-functional calculations are used in many branches of science to obtain information about the electronic structure of molecular systems and materials. Unfortunately, the traditional method for optimizing the Kohn-Sham energy suffers from fundamental problems that may lead to divergence or, even worse, convergence to an energy saddle point rather than to the ground-state minimum-in particular, for the larger and more complicated electronic systems that are often studied by Kohn-Sham theory nowadays. We here present a novel method for Kohn-Sham energy minimization that does not suffer from the flaws of the conventional approach, combining reliability and efficiency with linear complexity. In particular, the proposed method converges by design to a minimum, avoiding the sometimes spurious solutions of the traditional method and bypassing the need to examine the structure of the provided solution. 相似文献
223.
Petersen PB Roberts ST Ramasesha K Nocera DG Tokmakoff A 《The journal of physical chemistry. B》2008,112(42):13167-13171
Hydrogen-bonded interfaces are essential structural elements in biology. Furthermore, they can mediate electron transport by coupling the electron to proton transfer within the interface. The specific hydrogen-bonding configuration and strength have a large impact on the proton transfer, which exchanges the hydrogen-bonded donor and acceptor species (i.e., NH...O --> N...HO). Modulations of the hydrogen-bonding environment, such as the hydrogen-bond stretch and twist modes, affect the proton-transfer dynamics. Here, we present transient grating and echo peak shift measurements of the NH stretch vibrations of four doubly hydrogen-bonded cyclic dimers in their electronic ground state. The equilibrium vibrational dynamics exhibit strong coherent modulations that we attribute to coupling of the high-frequency NH vibration to the low-frequency interdimer stretch and twist modes and not to interference between multiple Fermi resonances that dominate the substructure of the linear spectra. 相似文献
224.
We present a fiber-based method for generating vortex beams with a tunable value of orbital angular momentum from -1? to +1? per photon. We propose a new (to our knowledge) method to determine the modal content of the fiber and demonstrate high purity of the desired vortex state (97% after 20 m, even after bends and twists). This method has immediate utility for the multitude of applications in science and technology that exploit vortex light states. 相似文献
225.
226.
Dr. Nicolas Menard Yohann Hériot Dr. Yves Le Mest Prof. Dr. Olivia Reinaud Dr. Nicolas Le Poul Dr. Benoît Colasson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10611-10618
The conformation of copper “funnel” complexes that contains a coordinating appended arm can be electrochemically switched between endo, which corresponds to the self‐coordination of the arm through the cavity, and exo positions. This process, which is reminiscent of a cup‐and‐ball device, is activated by an exogenous ligand for complexes that contain a hydroxy‐terminated arm. The exchange is electrochemically triggered and is operated in either CuI or CuII redox states, depending on the exogenous ligand, that is, CO or n‐butylamine, respectively. 相似文献
227.
This review is giving a short introduction to the techniques used to investigate isotope effects on NMR chemical shifts. The review is discussing how isotope effects on chemical shifts can be used to elucidate the importance of either intra- or intermolecular hydrogen bonding in ionic liquids, of ammonium ions in a confined space, how isotope effects can help define dimers, trimers, etc., how isotope effects can lead to structural parameters such as distances and give information about ion pairing. Tautomerism is by advantage investigated by isotope effects on chemical shifts both in symmetric and asymmetric systems. The relationship between hydrogen bond energies and two-bond deuterium isotope effects on chemical shifts is described. Finally, theoretical calculations to obtain isotope effects on chemical shifts are looked into. 相似文献
228.
Asger Halkier Henrik Koch Poul Jørgensen Ove Christiansen Ida M. Beck Nielsen Trygve Helgaker 《Theoretical chemistry accounts》1997,97(1-4):150-157
A systematic, high-level ab initio investigation of the water dimer has been performed. The oxygen-oxygen bond distance has
been estimated to be around 2.90 ?, about 0.05 ? shorter than the experimentally estimated distance, challenging the accuracy
of the latter. The interaction energy has been obtained at −5.0±0.1 kcal/mol, which compares favourably with the experimentally
estimated value of −5.4±0.7 kcal/mol. The importance of employing basis sets that include diffuse functions in correlated
calculations on hydrogen-bonded systems is confirmed. In correlated calculations on the water dimer and the hydrogen fluoride
dimer, the counterpoise-corrected interaction energies converge considerably slower towards the basis set limit than do the
uncorrected energies, provided that the correlation-consistent basis sets are augmented with diffuse functions.
Received: 12 February 1997 / Accepted: 5 June 1997 相似文献