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  • E. N. Voloshina and Yu. S. Dedkov, Electronic and Magnetic Properties of the Graphene- Ferromagnet Interfaces: Theory vs. Experiment, in Physics and Applications of Graphene - Experiments, ed. S. Mikhailov, INTECH Open, Vienna (2011) ISBN 978-953-307-217-3
  • C. Erk, L. Hammerschmidt, D. Andrae, B. Paulus and S. Schlecht, Low-temperature formation of cubic β-PbF2: precursor-based synthesis and first-principles phase stability study, Phys. Chem. Chem. Phys. 13, 6029 (2011). DOI: 10.1039/C0CP01758B

A precursor-based approach to the cubic β-phase of PbF2 was developed and allowed the preparation of this high-temperature phase well below the temperature for transition from the orthorhombic α- to the cubic β-phase. The formation of β-PbF2 from the molecular precursors Pb[Se(C6H2(CF3)3)]2 and Pb(C6H2(CF3)3)2 is facilitated by the presence of several short PbF contacts in these molecules. The cubic form of PbF2 was obtained as macroscopic crystals as well as nanoparticulate powder. Its formation at relatively low temperature suggested a theoretical re-investigation of the phase stabilities of the two polymorphs. The theoretical results from the Kohn–Sham density functional theory indicate that the energy content for the β-phase is slightly lower than the one for the α-phase, by 0.5–1.7 kJ mol−1 depending on the density functional used (zero-point vibrational energy correction included).

  • V. Koch and D. Andrae, "Static electric dipole polarizabilities for isoelectronic sequences", Int. J. Quantum Chem. 111, 891 (2011). DOI: 10.1002/qua.22911
    ☆ Special Issue: Dedicated to David Bishop

Static electric dipole polarizabilities αd(Z,N) from numerical nonrelativistic restricted Hartree-Fock (RHF) finite-field calculations for closed-shell atoms and isoelectronic ions with N ≤ 120 electrons are presented. For those sequences where the electronic ground state of the neutral or nearly neutral members is conserved upon increase of the nuclear charge number Z, i.e., for the nine sequences with N = 2, 4, 10, 12, 18, 28, 30, 36, or 46 electrons, systems with total charge number Q = Z − N varying in the range − 1 ≤ Q ≤ 90 were considered and their polarizability data fitted to rational functions of Q, with maximum absolute value of the relative error below 3%. The results presented here provide reference data (i) for algebraic approaches relying on basis functions and (ii) for the discussion of relativistic and correlation effects on polarizabilities along isoelectronic sequences.

  • D. Tietze, St. Voigt, D. Mollenhauer, M. Tischler, D. Imhof, T. Gutmann, L. González, O. Ohlenschläger, H. Breitzke, M. Görlach and G. Buntkowsky, Revealing the position of the substrate in NiSOD: a model study, Angew. Chem. Int. Ed. 50, 2946 (2011). DOI: 10.1002/anie.201005027
    in German: D. Tietze, St. Voigt, D. Mollenhauer, M. Tischler, D. Imhof, T. Gutmann, L. González, O. Ohlenschläger, H. Breitzke, M. Görlach and G. Buntkowsky, Bestimmung der Substratposition in der Nickel-Superoxiddismutase: eine Modellstudie, Angew. Chem. 123, 3002 (2011).
  • S. Böttcher, M. Weser, Yu. S. Dedkov, K. Horn, E. Voloshina, and B. Paulus, "Graphene on ferromagnetic surfaces and its functionalization with water and ammonia", Nanoscale Res. Lett. 6, 214 (2011). DOI:10.1186/1556-276X-6-214

In this article, an angle-resolved photoelectron spectroscopy (ARPES), X-ray absorption spectroscopy (XAS), and density-functional theory (DFT) investigations of water and ammonia adsorption on graphene/Ni(111) are presented. The results of adsorption on graphene/Ni(111) obtained in this study reveal the existence of interface states, originating from the strong hybridization of the graphene pi and spin-polarized Ni 3d valence band states. ARPES and XAS data of the H2O (NH3)/graphene/Ni(111) system give an information regarding the kind of interaction between the adsorbed molecules and the graphene on Ni(111). The presented experimental data are compared with the results obtained in the framework of the DFT approach.

  • M. Weser, E. N. Voloshina, K. Horn and Yu. S. Dedkov, Electronic structure and magnetic properties of the graphene/Fe/Ni(111) intercalation-like system, Phys. Chem. Chem. Phys. 13, 7534 (2011) DOI:10.1039/C1CP00014D

The electronic structure and magnetic properties of the graphene/Fe/Ni(111) system were investigated via combination of the density functional theory calculations and electron-spectroscopy methods. This system was prepared via intercalation of thin Fe layers (1 ML) underneath graphene on Ni(111) and its inert properties were verified by means of photoelectron spectroscopy. Intercalation of iron in the space between graphene and Ni(111) changes drastically the magnetic response from the graphene layer that is explained by the formation of the highly spin-polarized 3dz2 quantum-well state in the thin iron layer.

  • D. Andrae, I. Barth, T. Bredtmann, H.-C. Hege, J. Manz, F. Marquardt, and B. Paulus, Electronic quantum fluxes during pericyclic reactions exemplified for the cope rearrangement of semibullvalene, J. Phys. Chem. B, 115, 5476 (2011) DOI: 10.1021/jp110365g

The outcome of a pericyclic reaction is typically represented by arrows in the Lewis structure of the reactant, symbolizing the net electron transfer. Quantum simulations can be used to interpret these arrows in terms of electronic fluxes between neighboring bonds. The fluxes are decomposed into contributions from electrons in so-called pericyclic orbitals, which account for the mutation of the Lewis structure for the reactant into that for the product, in other valence and in core orbitals. Series of time-integrated fluxes of pericyclic electrons can be assigned to the arrows, for example 0.09-0.23 electrons for Cope rearrangement of semibullvalene, with hysteresis-type time evolutions for 27.3 fs. This means asynchronous electronic fluxes during synchronous rearrangement of all the nuclei. These predictions should become observable by emerging techniques of femto- to attosecond time-resolved spectroscopy.

  • D. Mollenhauer, J. Floß, H.-U. Reissig, E. Voloshina, and B. Paulus, Accurate quantum-chemical description of gold complexes with pyridine and its derivatives, J. Comput. Chem. 32, 1839 (2011) DOI: 10.1002/jcc.21765

Interaction of gold with pyridine and its derivatives was studied by means of different wavefunction-based correlation methods and standar DFT functionals as well as accounting for dispersion correction. Comparison of the calculated binding energies with benchmark CCSD(T)results allows us to find an appropriate computational method, when considering the two structures reflecting the interaction of gold with the lone pair at nitrogen, on the one hand, and with the π-system of pyridine, on the other hand. Additional binding sites were evaluated, when performing potential energy surface calculations and structure optimizations. The enhancement of the interaction energy due to donor substituents in the 4-position of the pyridine molecule has been investigated.

  • H. Lange, J. Maultzsch, W. Meng, D. Mollenhauer, B. Paulus, N. Peica, S. Schlecht, and C. Thomsen,"Adsorption Behavior of 4-Methoxypyridine on Gold Nanoparticles", Langmuir, 27, 7258 (2011) DOI: 10.1021/la200919m

We demonstrate a phase transfer method to create stable colloidal solutions of Au nanoparticles with 4-methoxypyridine ligands. We then investigate the adsorption behavior of 4-methoxypyridine onto gold surfaces by Raman spectroscopy, DFT calculations, and 1H NMR. In contrast to unsubstituted pyridine and the frequently used (N,N-dimethylamino)pyridine (DMAP), a flat adsorption of 4-methoxypyridine on gold was found.

  • Zh. Lu, C. Müller, Z. Yang, K. Hermansson and J. Kullgren, "SOx on ceria from adsorbed SO2", J. Chem. Phys. 134, 184703 (2011); DOI: 10.1063/1.3566998

Results from first-principles calculations present a rather clear picture of the interaction of SO2 with unreduced and partially reduced (111) and (110) surfaces of ceria. The Ce3+/Ce4+ redox couple, together with many oxidation states of S, give rise to a multitude of SOx species, with oxidation states from + III to + VI. SO2 adsorbs either as a molecule or attaches via its S-atom to one or two surface oxygens to form sulfite (SO32-) and sulfate (SO42-) species, forming new S-O bonds but never any S-Ce bonds. Molecular adsorption is found on the (111) surface. SO32- structures are found on both the (111) and (110) surfaces of both stoichiometric and partially reduced ceria. SO42-structures are observed on the (110) surface together with the formation of two reduced Ce3+ surface cations. SO2 can also partially heal the ceria oxygen vacancies by weakening a S-O bond, when significant electron transfer from the surface (Ce 4f) into the lowest unoccupied molecular orbital of the SO2 adsorbate takes place and oxidizes the surface Ce3+ cations. Furthermore, we propose a mechanism that could lead to monodentate sulfate formation at the (111) surface.

  • E. Voloshina, D. Mollenhauer, L. Chiappisi, and B. Paulus, "Theoretical study on the adsorption of pyridine derivatives on graphene", Chem. Phys. Lett. 510, 220 (2011) DOI:10.1016/j.cplett.2011.05.025

The adsorption of pyridine and its derivatives on the graphene surface has been studied using density functional theory (DFT). Adsorption geometries and energies as well as nature of binding have been analyzed. Dispersion effects have been taken into account via a semiempirical DFT-D2 method. Influence of electron-donor and electron-acceptor substituents in 4-position of the heterocyclic ring, effect of substrate and adsorbate’s concentration on the interaction energy have been investigated. Impact of the pyridine adsorption on the electronic band structure of graphene has been studied.

  • Yu. S. Dedkov, A. Generalov, E. N. Voloshina, and M. Fonin, "Structural and electronic properties of Fe3O4/graphene/Ni(111) junctions", Phys. Status Solidi RRL 5, 226 (2011); DOI 10.1002/pssr.201105197

The Fe3O4(111)/graphene/Ni(111) trilayer is proposed to be used as an ideal spin-filtering sandwich where the half-metallic properties of magnetite are used. Thin magnetite layers on graphene/Ni(111) were prepared via successive oxidation of a thin iron layer predeposited on graphene/Ni(111) and the formed system was investigated by means of low-energy electron diffraction and photoelectron spectroscopy. The electronic structure and structural quality of the graphene film sandwiched between two ferromagnetic layers remain unchanged upon magnetite formation as confirmed by experimental data.

  • E. Voloshina, D. Usvyat, M. Schütz, Yu. S. Dedkov, and B. Paulus, "On the physisorption of water on graphene: a CCSD(T) study", Phys. Chem. Chem. Phys. 13, 12041 (2011) DOI:10.1039/C1CP20609E
    ☆ The article was selected by editors for the “Editors Choice: Theoretical and Computational Chemistry” collection (see: PCCP Blog)

The electronic structure of the zero-gap two-dimensional graphene has a charge neutrality point exactly at the Fermi level that limits the practical application of this material. There are several ways to modify the Fermi-level-region of graphene, e.g. adsorption of graphene on different substrates or different molecules on its surface. In all cases the so-called dispersion or van der Waals interactions can play a crucial role in the mechanism, which describes the modification of electronic structure of graphene. The adsorption of water on graphene is not very accurately reproduced in the standard density functional theory (DFT) calculations and highly-accurate quantum-chemical treatments are required. A possibility to apply wavefunction-based methods to extended systems is the use of local correlation schemes. The adsorption energies obtained in the present work by means of CCSD(T) are much higher in magnitude than the values calculated with standard DFT functional although they agree that physisorption is observed. The obtained results are compared with the values available in the literature for binding of water on the graphene-like substrates.

  • C. Müller, D. Usvyat and H. Stoll, "Local correlation methods for solids: Comparison of incremental and periodic correlation calculations for the argon fcc crystal", Phys. Rev. B 83, 245136 (2011) DOI:10.1103/PhysRevB.83.245136

The correlation contribution to the cohesive energy of the Ar face-centered cubic (fcc) crystal has been evaluated within periodic and finite cluster models, using wave-function-based correlation techniques. The periodic local second-order Møller-Plesset perturbation (MP2) method is compared, in terms of accuracy and efficiency, to the incremental scheme employing standard MP2, local MP2, and local coupled cluster [CCSD(T)] methods. Three different finite cluster models of increasing complexity have been used in the incremental calculations. The local MP2 treatment is found to be relatively insensitive to the choice of the cluster model, and it is shown that within the LMP2 treatment virtually identical results can be expected from the periodic and different incremental calculations. Moreover, the two approaches can be considered as complementary: The periodic treatment allows for a relatively inexpensive reference, while further improvement of the level of correlation treatment and the size of one-particle basis sets is achieved more easily within the incremental scheme.

  • T. Bredtmann, S. Chelkowski, A. Bandrauk, "Monitoring attosecond dynamics of coherent electron-nuclear wave packets by molecular high-order-harmonic generation", Phys. Rev. A 84, 021401(R) (2011) DOI:10.1103/PhysRevA.84.021401

A pump-probe scheme for preparing and monitoring electron-nuclear motion in a dissociative coherent electron-nuclear wave packet is explored from numerical solutions of a non-Born-Oppenheimer time-dependent Schrödinger equation. A mid-ir intense few-cycle probe pulse is used to generate molecular high-order-harmonic generation (MHOHG) from a coherent superposition of two or more dissociative coherent electronic-nuclear wave packets, prepared by a femtosecond uv pump pulse. Varying the time delay between the intense ir probe pulse and the uv pump pulse by a few hundreds of attoseconds, the MHOHG signal intensity is shown to vary by orders of magnitude, thus showing the high sensitivity to electron-nuclear dynamics in coherent electron-nuclear wave packets. We relate this high sensitivity of MHOHG spectra to opposing electron velocities (fluxes) in the electron wave packets of the recombining (recolliding) ionized electron and of the bound electron in the initial coherent superposition of two electronic states.

  • A. R. R. Carvalho, A. Kenfack, F. Toscano, J. M. Rost, and A. M. Ozorio de Almeida: "Gaussian representation of extended quantum states" Phys. Lett. A 376, 19 (2011) DOI:10.1016/j.physleta.2011.10.029

Excited energy eigenstates and their superpositions typically exhibit a fine oscillatory structure near caustics. Semiclassical theory accesses these, but depends on detailed geometrical knowledge of the caustics. Here we show that a finite placement of coherent states on the classical region efficiently fits such extended states, reproducing structures that are much finer than the Gaussian width of the basis states. An extended state, evolved such that it becomes fully distinguishable from the original state, can also be faithfully reproduced by this finite basis. The ideal fitting follows from the projection of the extended state on the finite Hilbert space spanned by the Gaussians, rather than any discretization of the continuous (overcomplete) coherent state representation.

  • T. Bredtmann and J. Manz: "Electronic bond-to-bond fluxes in pericyclic reactions: synchronous or asynchronous?", Angew. Chem. Int. Ed. 50, 12652 (2011) DOI:10.1002/anie.201104465
  • E. N. Voloshina, A. Generalov, M. Weser, S. Böttcher, K. Horn, and Yu. S. Dedkov: "Structural and electronic properties of the graphene/Al/Ni(111) intercalation system", New J. Phys. 13, 113028 (2011) DOI:10.1088/1367-2630/13/11/113028

Decoupling of the graphene layer from the ferromagnetic substrate via intercalation of sp metal has recently been proposed as an effective way to realize a single-layer graphene-based spin-filter. Here, the structural and electronic properties of the prototype system, graphene/Al/Ni(111), are investigated via a combination of electron diffraction and spectroscopic methods. These studies are accompanied by state-of-the-art electronic structure calculations. The properties of this prospective Al-intercalation-like system and its possible implementations in future graphene-based devices are discussed.

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