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We study pump–probe schemes for the real time observation of electronic motion on attosecond time scale in the molecular ion H_{2}^{+} and its heavier isotope T_{2}^{+} while these molecules dissociate on femtosecond time scale by solving numerically the nonBorn–Oppenheimer timedependent Schrödinger equation. The UV pump laser pulse prepares a coherent superposition of the three lowest lying quantum states and the timedelayed midinfrared, intense fewfemtosecond probe pulse subsequently generates molecular highorder harmonics (MHOHG) from this coherent electron–nuclear wavepacket (CENWP). Varying the pump–probe time delay by a few hundreds of attoseconds, the MHOHG signal intensity is shown to vary by orders of magnitude. Due to nuclear movement, the coherence of these two upper states and the ground state is lost after a few femtoseconds and the MHOHG intensity variations as function of pump–probe delay time are shown to be equal to the period of electron oscillation in the coherent superposition of the two upper dissociative quantum states. Although this electron oscillation period and hence the periodicity of the harmonic spectra are quite constant over a wide range of internuclear distances, a strong signature of nuclear motion is seen in the actual shapes and ways in which these spectra change as a function of pump–probe delay time, which is illustrated by comparison of the MHOHG spectra generated by the two isotopes H_{2}^{+} and T_{2}^{+}. Two different regimes corresponding roughly to internuclear distances R < 4a_{0} and R > 4a_{0} are identified: For R < 4a_{0}, the intensity of a whole range of frequencies in the plateau region is decreased by orders of magnitude when the delay time is changed by a few hundred attoseconds whereas in the cutoff region the peaks in the MHOHG spectra are redshifted with increasing pump–probe time delay. For R > 4a_{0}, on the other hand, the peaks both in the cutoff and plateau region are redshifted with increasing delay times with only slight variations in the peak intensities. A time–frequency analysis shows that in the case of a twocycle probe pulse the sole contribution of one long and associated short trajectory correlates with the attenuation of a whole range of frequencies in the plateau region for R < 4a_{0} whereas the observed red shift for R > 4a_{0}, even in the plateau region, correlates with a single electron return within onehalf laser cycle.
The oxidative addition of HF at trans[Ir(Ar^{F})(η^{2}C_{2}H_{4})(PiPr_{3})_{2}] (1a: Ar^{F} = 4C_{5}NF_{4}; 1b: Ar^{F} = 2C_{6}H_{3}F_{2}) affords the fluorido complexes trans[Ir(Ar^{F})(F)(H)(PiPr_{3})_{2}] (2a: Ar^{F} = 4C_{5}NF_{4}; 2b: Ar^{F} = 2C_{6}H_{3}F_{2}). The hydrido fluorido complex 2a is also accessible by means of the reaction of the hydroxido complex trans[Ir(4C_{5}NF_{4})(H)(OH)(PiPr_{3})_{2}] (3a) with Et_{3}N·3HF. Both compounds 2a and 2b react with CO to give the carbonyl complexes trans[Ir(4C_{5}NF_{4})(F)(H)(CO)(PiPr_{3})_{2}] (4a: Ar^{F} = 4C_{5}NF_{4}; 4b: Ar^{F} = 2C_{6}H_{3}F_{2}). In the presence of traces of water, a slow reaction of 2a with CO_{2} yields the hydrogencarbonato complex trans[Ir(4C_{5}NF_{4})(H)(κ^{2}(O,O)O_{2}COH)(PiPr_{3})_{2}] (5a). Upon using 2a or 2b as fluorinating agent, Ph_{3}SiH could be converted into Ph3SiF and CH_{3}C(O)Cl into CH_{3}C(O)F.
A series of various tris(2,2'bithiophen5yl)aromatic derivatives were synthesized by Stille crosscoupling procedure. Their structures were characterized by ^{1}H NMR, ^{13}C NMR, and elemental analysis. DFT calculations for monomers were also performed. The optical properties of the synthesized materials as well as their energy levels were investigated by UV–vis absorption supported by fluorescence spectra and CV analysis. Oligomers obtained in the process of electropolymerization, possess a tetrathienyl bond with various aromatic and heteroaromatic cores. Electrochemical results confirm that the gained materials can apply successfully for a diversity of organic–electronic devices like organic lightemitting diodes (OLEDs), organic fieldeffect transistors (OFETs), and organic solar cells.
Strong electric fields open new routes for the control of radiationless decay in molecules with conical intersections. Here, we present quantum chemical and quantum dynamical simulations which demonstrate that the radiationless decay and related photoisomerization of pyridinylidenephenoxide can be effectively manipulated with strong electric fields by shifting the conical intersection. Moreover, we show the effects of the electric field on the orientation of the molecules and on the photoexcitation and discuss the conditions for which the field induced coupling between rotational and vibronic states can be neglected.
We explore the possibility of controlling rotationaltorsional dynamics of nonrigid molecules with strong, nonresonant laser pulses and demonstrate that transient, laserinduced torsional alignment depends on the nuclear spin of the molecule. Consequently, nuclear spin isomers can be manipulated selectively by a sequence of timedelayed laser pulses. We show that two pulses with different polarization directions can induce either overall rotation or internal torsion, depending on the nuclear spin. Nuclear spin selective control of the angular momentum distribution may open new ways to separate and explore nuclear spin isomers of polyatomic molecules.
If the BornOppenheimer approximation is invoked for the description of chemical reactions, the electron density rearranges following the motion of the nuclei. Even though this approach is central to theoretical chemistry, the explicit time dependence of the electron density is rarely studied, especially if the nuclei are treated quantum mechanically. In this article, we model the motion of benzene along the Kekulé vibrational coordinate to simulate the nuclear dynamics and electron density dynamics in the electronic ground state. Details of the change of core, valence, and π electrons are determined and analyzed. We show how the pictures anticipated by drawing Lewis structures of the rearrangement correlate with the timedependent quantum description of the process.
The present paper contributes to the construction of a “blackbox” 3D solver for the Hartree–Fock equation by the gridbased tensorstructured methods. It focuses on the calculation of the Galerkin matrices for the Laplace and the nuclear potential operators by tensor operations using the generic set of basis functions with low separation rank, discretized on a fine N×N×N Cartesian grid. We prove the Ch^{2} error estimate in terms of mesh parameter, h=O(1/N), that allows to gain a guaranteed accuracy of the core Hamiltonian part in the Fock operator as h→0. However, the commonly used problem adapted basis functions have low regularity yielding a considerable increase of the constant C, hence, demanding a rather large gridsize N of about several tens of thousands to ensure the high resolution. Modern tensorformatted arithmetics of complexity O(N), or even O(logN), practically relaxes the limitations on the gridsize. Our tensorbased approach allows to improve significantly the standard basis sets in quantum chemistry by including simple combinations of Slatertype, local finite element and other basis functions. Numerical experiments for moderate size organic molecules show efficiency and accuracy of gridbased calculations to the core Hamiltonian in the range of grid parameter N^{3}10^{15}.
Highly accurate methods such as coupled cluster (CC) techniques can be used for periodic systems within the framework of the method of increments. Its extension to a lowdimensional conducting system is considered. To demonstrate the presented approach, a clean Mg(0001) surface is selected, where the CC treatment with single and double excitations and perturbative triples is used for calculation of the surface energy. A further example concerns the adsorption energy of Xe on the metal surface. The obtained results can be used to verify the performance of the approximate methods. Along with the computational speedup at the high level of accuracy, application of the method of increments provides for a possibility to analyze the influence of individual correlation energy increments on the studied property.
We present quantum simulations of a vibrating hydrogen molecule H_{2} and address the issue of electron correlation. After appropriately setting the frame and the observer plane, we were able to determine precisely the number of electrons and nuclei which actually flow by evaluating electronic and nuclear fluxes. This calculation is repeated for three levels of quantum chemistry, for which we account for no correlation, HartreeFock, static correlation, and dynamic correlation. Exciting each of these systems with the same amount of energy, we show that the electron correlation can be revealed with the knowledge of quantum fluxes. This is evidenced by a clear sensitivity of these fluxes to electron correlation. In particular, we find that this correlation remarkably enhances more electronic yield than the nuclear one. It turns out that less electrons accompany the nuclei in HartreeFock than in the correlation cases.
We study numerically pumpprobe schemes for monitoring electronnuclear motion in a dissociating molecule using a midinfrared, intense fewfemtosecond probe laser pulse which generates molecular highorder harmonics (MHOHG) from a coherent superposition of electronnuclear wave packets prepared by a weak femtosecond UV pump pulse from an initial bound state. We show that by varying the time delay between the intense probe pulse and the UV pump pulse by a few hundred attoseconds one alters the MHOHG signal intensity by many orders of magnitude. The periodicity of the MHOHG intensity variations as function of the time delay is equal to the period of the electron oscillation in the coherent superposition which varies with internuclear distance. We use the strong field approximation (SFA) and threestep model to explain this high sensitivity of the harmonic intensity to pulse delay time and to the overlap of nuclear wave packets. We also solve numerically the threedimensional (3D) timedependent Schrödinger equation describing harmonic generation for a hydrogen atom prepared in a superposition of its two lowest atomic states, in order to investigate the dependence of the same effect (in a simpler system but in 3D) on the probepulse carrierenvelope phase (CEP) and on the probe duration. We also relate these strong effects in the intensity of harmonics to the correlation between the velocity of the recolliding electron wave packet and the electron velocity in the coherent superposition of the electron bound states.
This article presents the results of the first quantum simulations of the electronic flux density (j_{e}) by the “coupledchannels”(CC) theory, the fundamentals of which are presented in the previous article [Diestler, D. J. J. Phys. Chem. A 2012, DOI: 10.1021/jp207843z]. The principal advantage of the CC scheme is that it employs exclusively standard methods of quantum chemistry and quantum dynamics within the framework of the Born–Oppenheimer approximation (BOA). The CC theory goes beyond the BOA in that it yields a nonzero je for electronically adiabatic processes, in contradistinction to the BOA itself, which always gives j_{e} = 0. The CC is applied to oriented H_{2}^{+} vibrating in the electronic ground state (^{2}Σ_{g}^{+}), for which the nuclear and electronic flux densities evolve on a common time scale of about 22 fs per vibrational period. The system is chosen as a touchstone for the CC theory, because it is the only one for which highly accurate flux densities have been calculated numerically without invoking the BOA [Barth et al, Chem. Phys. Lett. 2009, 481, 118]. Good agreement between CC and accurate results supports the CC approach, another advantage of which is that it allows a transparent interpretation of the temporal and spatial properties of j_{e}.
Pericyclic reactions in the electronic ground state may be initiated by downchirped pumpdump subpulses of an optimal laser pulse, in the ultraviolet (UV) frequency and sub10 femtosecond (fs) time domain. This is demonstrated by means of a quantum dynamics model simulation of the Cope rearrangement of Semibullvalene. The laser pulse is designed by means of optimal control theory, with detailed analysis of the mechanism. The theoretical results support the recent experimental initiation of a pericyclic reaction. The present approach provides an important step towards monitoring asynchronous electronic fluxes during synchronous nuclear pericyclic reaction dynamics, with femtotoattosecond time resolution, as motivated by the recent prediction of our group.
We have performed CCSD(T), MP2, and DFLMP2 calculations of the interaction energy of CO on the MgF_{2} (110) surface by applying the method of increments and an embedded cluster model. In addition, we performed periodic HF, B3LYP, and DFLMP2 calculations and compare them to the cluster results. The incremental CCSD(T) calculations predict an interaction energy of E_{int} = −0.37 eV with a Cdown orientation of CO above a Mg^{2+} ion at the surface with a basis set of VTZ quality. We find that electron correlation constitutes about 50 % of the binding energy and a detailed evaluation of the increments shows that the largest contribution to the correlation energy originates from the CO interaction with the closest F ions on the second layer.
In this article we provide an overview of the most common ways of treating electron correlation effects in 3Dperiodic systems with some emphasize on wavefunctionbased correlation methods such as the method of increments and the local MP2 method implemented in the CRYSCOR program. We discuss strengths and weaknesses of the different approaches and give examples for their application. Additionally, for the method of increments we discuss recent developments for its application to open shell systems and problems related to the treatment of graphene sheets. M. J. Molski, D. Mollenhauer, S. Gohr, B. Paulus, M. A. Khanfar, H. Shorafa, S. H. Strauss, K. Seppelt: Halogenated Benzene Cation Radicals, Chem. Eur. J., 18(21), 6644 (2012). Link The halogenated benzenes C_{6}HF_{5}, 2,4,6C_{6}H_{3}F_{3}, 2,3,5,6C_{6}H_{2}F_{4}, C_{6}F_{6}, C_{6}Cl_{6}, C_{6}Br_{6}, and C_{6}I_{6} were converted into their corresponding cation radicals by using various strong oxidants. The cationradical salts were isolated and characterized by electron paramagnetic resonance (EPR) spectroscopy and by singlecrystal Xray diffraction. The thermal stability of the cation radicals increased with decreasing hydrogen content. As expected, the cation radicals [C_{6}HF_{5}]+ and 2,3,5,6[C_{6}H_{2}F_{4}]^{+} had structures with the same geometry as C_{6}HF_{5} and 2,3,5,6[C_{6}H_{2}F_{4}]. In contrast, the cation radicals [C_{6}F_{6}]^{+}, [C_{6}Cl_{6}]^{+}, and possibly also [C_{6}Br_{6}]^{+} exhibited Jahn–Tellerdistorted geometries in the crystalline state. In the case of C_{6}F_{6}^{+}Sb_{2}F_{11}^{−}, two lowsymmetry geometries were observed in the same crystal. Interestingly, the structures of the cation radicals 2,4,6[C_{6}H_{3}F_{3}]^{+} and C_{6}I_{6}^{+} did not exhibit Jahn–Teller distortions. DFT calculations showed that the explanation for the lack of distortion of these cations from the D3h or D6h symmetry of the neutral benzene precursor was different for 2,4,6[C_{6}H_{3}F_{3}]^{+} than for [C_{6}I_{6}]^{+}.
The electronic and crystallographic structure of the graphene/Rh(111) moiré lattice is studied via combination of densityfunctional theory calculations and scanning tunneling and atomic force microscopy (STM and AFM). Whereas the principal contrast between hills and valleys observed in STM does not depend on the sign of applied bias voltage, the contrast in atomically resolved AFM images strongly depends on the frequency shift of the oscillating AFM tip. The obtained results demonstrate the perspectives of application atomic force microscopy/spectroscopy for the probing of the chemical contrast at the surface.
The present manuscript summarizes the modern view on the problem of the graphene–metal interaction. Presently, the closepacked surfaces of d metals are used as templates for the preparation of highlyordered graphene layers. Different classifications can be introduced for these systems: graphene on latticematched and graphene on latticemismatched surfaces where the interaction with the metallic substrate can be either “strong” or “weak”. Here these classifications, with the focus on the specific features in the electronic structure in all cases, are considered on the basis of large amount of experimental and theoretical data, summarized and discussed. The perspectives of the graphene–metal interfaces in fundamental and applied physics and chemistry are pointed out.
We have computed the lattice structure, bulk modulus, electronic structure, and cohesive energies for the CoSb_{3} skutterudite by performing plane wave and atomic basis set DFT, as well as HF atomic basis set calculations. We find that plane wave and atomic basis set DFT calculations compare almost perfectly well. Band gaps vary significantly, depending on the applied functional and subtle changes of the lattice structure of CoSb_{3}. Where LDA strongly overestimates the binding, cohesive energies are reasonably well described by GGA and hybrid DFT functionals within 2 eV in comparison to experiment. HF results are unreasonably far off compared to DFT and experimental values for all calculated properties, which indicates that correlation effects play an important role in the characterization of skutterudites.

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This page was last modified on June 10, 2013, at 02:17 PM 