Christian Neiss

Publications (14)33.77 Total impact

• Article: Structures of small bismuth cluster cations.

  Rebecca Kelting, Alexander Baldes, Ulrike Schwarz, Thomas Rapps, Detlef Schooss, Patrick Weis, Christian Neiss, Florian Weigend, Manfred M Kappes
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  ABSTRACT: The structures of bismuth cluster cations in the range between 4 and 14 atoms have been assigned by a combination of gas phase ion mobility and trapped ion electron diffraction measurements together with density functional theory calculations. We find that above 8 atoms the clusters adopt prolate structures with coordination numbers between 3 and 4 and highly directional bonds. These open structures are more like those seen for clusters of semiconducting-in-bulk elements (such as silicon) rather than resembling the compact structures typical for clusters of metallic-in-bulk elements. An accurate description of bismuth clusters at the level of density functional theory, in particular of fragmentation pathways and dissociation energetics, requires taking spin-orbit coupling into account. For n = 11 we infer that low energy isomers can have fragmentation thresholds comparable to their structural interconversion barriers. This gives rise to experimental isomer distributions which are dependent on formation and annealing histories.
  The Journal of chemical physics 04/2012; 136(15):154309. · 3.09 Impact Factor
• Article: Laser-induced fluorescence of rhodamine 6G cations in the gas phase: a lower bound to the lifetime of the first triplet state.

  Mattias Kordel, Detlef Schooss, Christian Neiss, Lars Walter, Manfred M Kappes
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  ABSTRACT: We have studied the gas-phase laser-induced fluorescence of an ensemble of buffer gas-cooled Rhodamine 6G cations (R6G(+)) stored in a quadrupole ion trap at 90 K. The fluorescence resulting from excitation with continuous-wave 488 nm radiation was observed to disappear almost completely on a time scale of seconds, dependent in detail on the excitation laser fluence. Such decay can be explained by the accumulation of R6G(+) in a dark triplet state. This in turn facilitates the first lifetime determination of the lowest triplet state of free R6G(+) by direct ground-state recovery measurements. A lower bound for the half-life was found to be approximately 2 s. Adding oxygen in a volume fraction of 1% to the buffer gas leads to efficient quenching of the triplet state and correspondingly to complete suppression of the fluorescence intensity decay. Different rare gases were applied as buffers for collisional cooling, but no significant changes in the fluorescence properties were found.
  The Journal of Physical Chemistry A 04/2010; 114(17):5509-14. · 2.95 Impact Factor
• Article: Structure determination of gold clusters by trapped ion electron diffraction: Au(14)(-)-Au(19)(-).

  Anne Lechtken, Christian Neiss, Manfred M Kappes, Detlef Schooss
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  ABSTRACT: The structures of mass-selected gold cluster anions Au(14)(-)-Au(19)(-) have been reinvestigated using an improved low temperature trapped ion electron diffraction experiment. Structures were assigned by comparing experimental with simulated scattering functions using model structures obtained by density functional calculations. Flat three-dimensional structures are found for Au(14)(-) and Au(15)(-), hollow cages for Au(16)(-)-Au(18)(-) and a tetrahedral structure is found for Au(19)(-). For several clusters in this series, our assignments differ distinctly from previous assignments.
  Physical Chemistry Chemical Physics 07/2009; 11(21):4344-50. · 3.57 Impact Factor
• Article: Publisher's Note: ``Comparative study of the structures of copper, silver, and gold icosamers: Influence of metal type and charge state'' [J. Chem. Phys. 129, 154304 (2008)]

  Anne Lechtken, Christian Neiss, Jason Stairs, Detlef Schooss
  Chemical Physics 06/2009; 131(2):9901. · 1.90 Impact Factor
• Article: Comment on Quintuple-zeta quality coupled-cluster correlation energies with triple-zeta basis sets by D. P. Tew, W. Klopper, C. Neiss and C. Hättig, Phys. Chem. Chem. Phys., 2007, 9, 1921 [erratum].

  David P Tew, Wim Klopper, Christian Neiss, Christof Hättig
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  ABSTRACT: After rectifying a small programming error, CCSD(F12) correlation energies are even better than previously reported, particularly for double-zeta basis sets.
  Physical Chemistry Chemical Physics 12/2008; 10(41):6325-7. · 3.57 Impact Factor
• Article: Comparative study of the structures of copper, silver, and gold icosamers: Influence of metal type and charge state.

  Anne Lechtken, Christian Neiss, Jason Stairs, Detlef Schooss
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  ABSTRACT: We present a comparative study on the structural properties of the coinage metal icosamers Cu(20)(+/-), Ag(20)(+/-), and Au(20)(+/-). Using trapped ion electron diffraction measurements in combination with density functional structure calculations we find distinct structural differences depending on the cluster material and the charge state: Cu(20)(-), Cu(20)(+), as well as Ag(20)(+) prefer icosahedral structures. Ag(20)(-) adopts a rearranged, distorted icosahedral structure. While Au(20)(-) is tetrahedral, Au(20)(+) cannot be described satisfyingly by a single isomer alone. Here a mixture of tetrahedral and distorted icosahedral structures is suggested. The influence of material and charge on the structural properties of the coinage metal icosamers is discussed.
  The Journal of chemical physics 11/2008; 129(15):154304. · 3.09 Impact Factor
• Article: Synthesis, Characterization and Quantum Mechanical Calculations of [Au18Se8(dppthph)6]Cl2

  Paloma Sevillano, Olaf Fuhr, Oliver Hampe, Sergej Lebedkin, Christian Neiss, Reinhart Ahlrichs, Dieter Fenske, Manfred M. Kappes
  Berichte der deutschen chemischen Gesellschaft 10/2007; 2007(33):5163 - 5167. · 2.94 Impact Factor
• Article: Quintuple-zeta quality coupled-cluster correlation energies with triple-zeta basis sets.

  David P Tew, Wim Klopper, Christian Neiss, Christof Hättig
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  ABSTRACT: The explicitly-correlated coupled-cluster method CCSD(T)(R12) is extended to include F12 geminal basis functions that decay exponentially with the interelectronic distance and reproduce the form of the average Coulomb hole more accurately than linear-r(12). Equations derived using the Ansatz 2 strong orthogonality projector are presented. The convergence of the correlation energy with orbital basis set for the new CCSD(T)(F12) method is studied and found to be rapid, 98% of the basis set limit correlation energy is typically recovered using triple-zeta orbital basis sets. The performance for reaction enthalpies is assessed via a test set of 15 reactions involving 23 molecules. The title statement is found to hold equally true for total and relative correlation energies.
  Physical Chemistry Chemical Physics 05/2007; 9(16):1921-30. · 3.57 Impact Factor
• Article: Frequency-dependent nonlinear optical properties with explicitly correlated coupled-cluster response theory using the CCSD(R12) model.

  Christian Neiss, Christof Hättig
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  ABSTRACT: Response theory up to infinite order is combined with the explicitly correlated coupled-cluster singles and doubles model including linear-r(12) corrections, CCSD(R12). The additional terms introduced by the linear-r(12) contributions, not present in the conventional CCSD calculation, are derived and discussed with respect to the extra costs required for their evaluation. An implementation is presented up to the cubic response function for one-electron perturbations, i.e., up to frequency-dependent second hyperpolarizabilities. As first applications the authors computed the electronic polarizabilities and second hyperpolarizabilities of BH, N(2), and formaldehyde and show that the improvement in the one-electron basis set convergence known from the R12 method for ground state energies is retained for higher-order optical properties. Frequency-dependent results are presented for the second hyperpolarizability of N(2).
  The Journal of Chemical Physics 05/2007; 126(15):154101. · 3.33 Impact Factor
• Article: Extensions of r12 corrections to CC2-R12 for excited states.

  Christian Neiss, Christof Hättig, Wim Klopper
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  ABSTRACT: As known since about two decades, R12 methods, which include terms linear in the interelectronic distance r(12) in the wave function, improve substantially the basis set convergence of the ground state correlation energy. In a previous study, however, it was found that the same approach does not give a similar systematic improvement if applied to excited states in the framework of coupled cluster response theory. In the present work, we examine the reason for this behavior and show that the inclusion of additional orbitals in the construction of the r(12) pair functions leads to an enhanced basis set convergence (and thus a balanced description) also for the excited states.
  The Journal of Chemical Physics 09/2006; 125(6):64111. · 3.33 Impact Factor
• Article: Molecular Dynamics Simulation of the LOV2 Domain from

  Christian Neiss, Peter Saalfrank
  Journal of Chemical Information and Modeling. 01/2004; 44:1788-1793.
• Article: Ab initio quantum chemical investigation of the first steps of the photocycle of phototropin: a model study.

  Christian Neiss, Peter Saalfrank
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  ABSTRACT: Phototropin is a blue light-activated photoreceptor that plays a dominant role in the phototropism of plants. The protein contains two subunits that bind flavin mononucleotide (FMN), which are responsible for the initial steps of the light-induced reaction. It has been proposed that the photoexcited flavin molecule adds a cysteine residue of the protein backbone, thus activating autophosphorylation of the enzyme. In this study, the electronic properties of several FMN-related compounds in different charge and spin states are characterized by means of ab initio quantum mechanical calculations. The model compounds serve as idealized model chromophores for phototropism. Reaction energies are estimated for simple model reactions, roughly representing the addition of a cysteine residue to the flavin molecule. Excitation energies were calculated with the help of time-dependent density functional theory. On the basis of these calculations we propose the following mechanism for the addition reaction: (1) after photoexcitation of FMN out of the singlet ground state S0, excited singlet state(s) are populated; these relax to the lowest excited singlet state S1, and subsequently by intersystem crossing FMN in the lowest triplet state, T1 is formed; (2) the triplet easily removes the neutral hydrogen atom from the H-S group of the cysteine residue; and (3) the resulting thio radical is added.
  Photochemistry and Photobiology 02/2003; 77(1):101-9. · 2.41 Impact Factor
• Article: Quantum Chemical Calculation of Excited States of Flavin-Related Molecules

  Christian Neiss, Peter Saalfrank, Maja Parac, Stefan Grimme
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  ABSTRACT: The performance of various methods of various quantum mechanical methods for the calculation of low-lying singlet and triplet excited states of biologically relevant species related to flavins is critically examined. In particular, configuration interaction singles (CIS), time-dependent density functional theory (TD-DFT), and the recently proposed multireference configuration interaction DFT method (DFT/MRCI) [Grimme, S.; Waletzke, M. J. Chem. Phys. 1999, 111, 5645] are compared. For the DFT-based methods, various hybrid exchange−correlation functionals are used. For the “test molecule” uracil, it is found that CIS does not give quantitatively accurate energies even in conjunction with large basis sets including diffuse functions. In contrast TD-DFT(B3LYP) and DFT/MRCI produce reasonably accurate results even with medium-sized basis sets such as 6-31G*. Following these test calculations, the absorption energies of the lumiflavin molecule in its ground (i.e., S0 → Sn) and lowest triplet state (i.e., T1 → Tn) are investigated. The nature of the low-lying excited states is discussed, and the results are compared to experiment. Finally, the effect of surrounding water molecules and of geometrical distortions on the absorption spectrum of flavin-type species is discussed on the basis of model calculations.
  12/2002;
• Article: Molecular dynamics simulation of the LOV2 domain from Adiantum capillus-veneris.

  Christian Neiss, Peter Saalfrank
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  ABSTRACT: The mechanism for signal transduction from the LOV-domains toward the kinase region of phototropin is still not well understood. We have performed molecular dynamics (MD) simulations and CONCOORD calculations on the LOV2 domain of Adiantum capillus-veneris, with the goal to detect possible differences between the two forms of the LOV domain which may not show up in the static crystal structures. Since no such clear differences are found in the MD simulations also, we suggest that the real, biologically active conformation of the LOV domain within the whole phototropin is different from the crystal structure of the isolated LOV domains. The MD simulations do offer, however, insight into details of the dynamics of the dark and illuminated LOV domains, which are discussed in the light of recent experiments.
  Journal of Chemical Information and Computer Sciences 44(5):1788-93.