Wilhelm Ostwald Institute For Physikalische Und Theoretische Chemie

Leipzig, Germany

Wilhelm Ostwald Institute For Physikalische Und Theoretische Chemie

Leipzig, Germany
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Marsalek O.,Czech Institute of Organic Chemistry And Biochemistry | Marsalek O.,Academy of Sciences of the Czech Republic | Uhlig F.,Wilhelm Ostwald Institute For Physikalische Und Theoretische Chemie | Jungwirth P.,Czech Institute of Organic Chemistry And Biochemistry | Jungwirth P.,Academy of Sciences of the Czech Republic
Journal of Physical Chemistry C | Year: 2010

Ab initio molecular dynamics simulations were performed with the aim to follow two scenarios for an excess electron in cold water clusters. In the first one, an electron is attached to a quenched neutral cluster. Such an electron, initially very delocalized and loosely bound, shrinks somewhat and increases its vertical detachment energy to 1 - 1.5 eV within several picoseconds. Unlike in warm liquid clusters, the electron in this cold system does not, however, reach a more compact and strongly bound structure. In contrast, if an equilibrated negatively charged water cluster with a well-localized excess electron is instantaneously quenched to ∼0 K, the electron remains strongly bound in a water cavity and practically does not change its size and binding energy. These results have important consequences for detailed interpretation of photoelectron spectroscopy measurements of electrons solvated in aqueous clusters and liquid water microjets. © 2010 American Chemical Society.


Marsalek O.,Czech Institute of Organic Chemistry And Biochemistry | Uhlig F.,Wilhelm Ostwald Institute For Physikalische Und Theoretische Chemie | Frigato T.,Free University of Berlin | Schmidt B.,Free University of Berlin | Jungwirth P.,Czech Institute of Organic Chemistry And Biochemistry
Physical Review Letters | Year: 2010

The process of electron localization on a cluster of 32 water molecules at 20, 50, and 300 K is unraveled using ab initio molecular dynamics simulations. In warm, liquid clusters, the excess electron relaxes from an initial diffuse and weakly bound structure to an equilibrated, strongly bound species within 1.5 ps. In contrast, in cold, glassy clusters the relaxation processes is not completed and the electron becomes trapped in a metastable surface state with an intermediate binding energy. These results question the validity of extrapolations of the properties of solvated electrons from cold clusters of increasing size to the liquid bulk. © 2010 The American Physical Society.


PubMed | Wilhelm Ostwald Institute For Physikalische Und Theoretische Chemie, University Claude Bernard Lyon 1, VU University Amsterdam and Scientific Computing and Modelling NV
Type: Journal Article | Journal: The Journal of chemical physics | Year: 2016

We report a time-dependent density functional based tight-binding (TD-DFTB) scheme for the calculation of UV/Vis spectra, explicitly taking into account the excitation of nuclear vibrations via the adiabatic Hessian Franck-Condon method with a harmonic approximation for the nuclear wavefunction. The theory of vibrationally resolved UV/Vis spectroscopy is first summarized from the viewpoint of TD-DFTB. The method is benchmarked against time-dependent density functional theory (TD-DFT) calculations for strongly dipole allowed excitations in various aromatic and polar molecules. Using the recent 3ob:freq parameter set of Elstners group, very good agreement with TD-DFT calculations using local functionals was achieved.


PubMed | VU University Amsterdam, Wilhelm Ostwald Institute For Physikalische Und Theoretische Chemie and Scientific Computing & Modelling NV
Type: Journal Article | Journal: The Journal of chemical physics | Year: 2016

We propose a new method of calculating electronically excited states that combines a density functional theory based ground state calculation with a linear response treatment that employs approximations used in the time-dependent density functional based tight binding (TD-DFTB) approach. The new method termed time-dependent density functional theory TD-DFT+TB does not rely on the DFTB parametrization and is therefore applicable to systems involving all combinations of elements. We show that the new method yields UV/Vis absorption spectra that are in excellent agreement with computationally much more expensive TD-DFT calculations. Errors in vertical excitation energies are reduced by a factor of two compared to TD-DFTB.


Thomas M.,University of Bonn | Brehm M.,Wilhelm Ostwald Institute For Physikalische Und Theoretische Chemie | Holloczki O.,University of Bonn | Kelemen Z.,Budapest University of Technology and Economics | And 3 more authors.
Journal of Chemical Physics | Year: 2014

The vibrational spectra of the ionic liquid 1-ethyl-3-methylimidazolium acetate and its mixtures with water and carbon dioxide are calculated using ab initio molecular dynamics simulations, and the results are compared to experimental data. The new implementation of a normal coordinate analysis in the trajectory analyzer TRAVIS is used to assign the experimentally observed bands to specific molecular vibrations. The applied computational approaches prove to be particularly suitable for the modeling of bulk phase effects on vibrational spectra, which are highly important for the discussion of the microscopic structure in systems with a strong dynamic network of intermolecular interactions, such as ionic liquids. © 2014 AIP Publishing LLC.


PubMed | University of Bonn, Wilhelm Ostwald Institute For Physikalische Und Theoretische Chemie, Eötvös Loránd University and Budapest University of Technology and Economics
Type: Journal Article | Journal: The Journal of chemical physics | Year: 2014

The vibrational spectra of the ionic liquid 1-ethyl-3-methylimidazolium acetate and its mixtures with water and carbon dioxide are calculated using ab initio molecular dynamics simulations, and the results are compared to experimental data. The new implementation of a normal coordinate analysis in the trajectory analyzer TRAVIS is used to assign the experimentally observed bands to specific molecular vibrations. The applied computational approaches prove to be particularly suitable for the modeling of bulk phase effects on vibrational spectra, which are highly important for the discussion of the microscopic structure in systems with a strong dynamic network of intermolecular interactions, such as ionic liquids.


Staiger M.,TU Berlin | Bacic V.,Jacobs University Bremen | Gillen R.,TU Berlin | Radovsky G.,Weizmann Institute of Science | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

We present Raman spectra of misfit layer (PbS)1.14NbS2 nanotubes and lead intercalated NbS2 nanotubes. They represent interesting model systems to investigate the nature of interlayer interaction in layered materials. A direct correlation to the Raman modes of the parent 2H-NbS2 compound exists, but some modes are seen drastically upshifted in frequency in the misfit layer and intercalated compound while others remain almost unchanged. On the basis of the Raman spectroscopic investigations and with the help of supporting calculations we examine different interlayer bonding mechanisms and contribute to the discussion as to why these frequency shifts occur. © 2016 American Physical Society.


Cremer T.,Friedrich - Alexander - University, Erlangen - Nuremberg | Kolbeck C.,Friedrich - Alexander - University, Erlangen - Nuremberg | Lovelock K.R.J.,University of Nottingham | Paape N.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 8 more authors.
Chemistry - A European Journal | Year: 2010

Ten [C8C1Im]+ (1-methyl-3- octylimidazolium)-based ionic liquids with anions Cl-, Br -, I-, [NO3]-, [BF4] -, [TfO]-, [PF6]-, [Tf 2N]-, [Pf2N]-, and [FAP]- (TfO = trifluoromethylsulfonate, Tf2N = bis(trifluoromethylsulfonyl) imide, Pf2N = bis(pentafluoroethylsulfonyl)imide, FAP = tris-(pentafluoroethyl)trifluorophosphate) and two [C8C 1C1Im]+ (1,2-dimethyl-3-octylimidazolium)-based ionic liquids with anions Br- and [Tf2N]- were investigated by using X-ray photoelectron spectroscopy (XPS), NMR spectroscopy and theoretical calculations. While1H NMR spectroscopy is found to probe very specifically the strongest hydrogen-bond interaction between the hydrogen attached to the C2 position and the anion, a comparative XPS study provides first direct experimental evidence for cation-anion charge-transfer phenomena in ionic liquids as a function of the ionic liquid's anion. These charge-transfer effects are found to be surprisingly similar for [C8C1Im]+ and [C8C1C 1Im]+ salts of the same anion, which in combination with theoretical calculations leads to the conclusion that hydrogen bonding and charge transfer occur independently from each other, but are both more pronounced for small and more strongly coordinating anions, and are greatly reduced in the case of large and weakly coordinating anions. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Thomas M.,University of Bonn | Brehm M.,Wilhelm Ostwald Institute For Physikalische Und Theoretische Chemie | Holloczki O.,University of Bonn | Kirchner B.,University of Bonn
Chemistry - A European Journal | Year: 2014

The solvation of the carbene 1-ethyl-3-methylimidazole-2-ylidene in the ionic liquid 1-ethyl-3-methylimidazolium acetate was investigated by ab initio molecular dynamics simulations in order to reveal the interaction between these two highly important classes of materials: N-heterocyclic carbenes with superb catalytic activity and ionic liquids with advantageous properties as solvents and reaction media. In contrast to previously published data on analogous systems, no hydrogen bond is observed between the hypovalent carbon atom and the most acidic ring hydrogen atoms, as these interaction sites of the imidazolium ring are predominantly occupied by the acetate ions. Keeping the carbene away from the ring hydrogen atoms prevents stabilization of this reactive species, and hence any retarding effect on subsequent reactions, which explains the observed high reactivity of the carbene in acetate-based ionic liquids. Instead, the carbene exhibits a weaker interaction with the methyl group of the imidazolium cation by forming a hitherto unprecedented kind of C×××HC hydrogen bond. This unexpected finding not only indicates a novel kind of hydrogen bond for carbenes, but also shows that such interaction sites of the imidazolium cation are not limited to the ring hydrogen atoms. Thus, the results give the solute-solvent interactions within ionic liquids a new perspective, and provide a further, albeit weak, site of interaction to tune in order to achieve the desired environment for any dissolved active ingredient. The methyl group in the game: When an N-heterocyclic carbene is dissolved in an imidazole-based ionic liquid, it cannot form hydrogen bonds with the ring hydrogen atoms of the cation if basic anions are present; therefore, it binds to a methyl group instead (see figure). The lack of strong hydrogen bonding keeps the carbene available for reactions. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Lach J.,University of Leipzig | Perlt E.,Wilhelm Ostwald Institute For Physikalische Und Theoretische Chemie | Kirchner B.,Wilhelm Ostwald Institute For Physikalische Und Theoretische Chemie | Kersting B.,University of Leipzig
Zeitschrift fur Anorganische und Allgemeine Chemie | Year: 2013

The preparation and characterization of three new mixed ligand macrocyclic [Ni2L2(L')]+ complexes are described, where (L2) 2- represents a supporting macrocyclic hexaaza-bis(phenylsulfonato) ligand and L' a tetrazolato ligand. The complexes [Ni2(L2)(CN 4H)]BPh4 (4), [Ni2(L2)(CN4Me)] BPh4 (5), and [Ni2(L2)(CN4Ph)]BPh4 (6) were synthesized by H2O2 oxidation of the corresponding [Ni2(L1)(CN4H)]BPh4 (1), [Ni 2(L1)(CN4Me)]BPh4 (2), and [Ni 2(L1)(CN4Ph)]BPh4 (3) complexes supported by the corresponding hexaaza-bis(thiophenolate) macrocycle. The compounds were characterized by means of elemental analysis, mass spectrometry, IR, and UV/Vis spectroscopy. The crystal structures of compounds 4-6 show that the bridging thiophenolate functions in 1-3 are in all cases converted to μ 1, 3-bridging sulfonate groups to generate N3Ni(μ 1, 3-SO3R)2(μ-RCN4)NiN 3 cores. The conversion to the phenylsulfonato groups is accompanied by a drastic increase of the Ni⋯Ni distances from 3.455(1) Å in 1, 3.425(1) Å in 2, and 3.443(1) Å [3.450(1) Å] in 3 to 4.2796(5) Å [4.3375(6) Å] in 4, 4.3402(6) Å in 5, and 4.2607(4) Å in 6. Upon oxidation the magnetic properties are affected. In contrast to 1-3, which exhibit an intramolecular ferromagnetic exchange interaction (S = 2 ground state), the spins of the nickel(II) (Si = 1) ions in 4-6 are antiferromagnetically coupled, the coupling constants J being -1.39 cm -1 (4), -1.43 cm-1 (5), and -1.60 cm-1 (6) (H = -2JS1S2) to yield a diamagnetic S = 0 ground state. DFT (density functional theory) calculations were carried out to substantiate the experimental results. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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