Publications (193) View all
-
Article: Analysis of differences in oxygen sensitivity of Fe-S clusters.
[show abstract] [hide abstract]
ABSTRACT: Many but not all iron-sulphur clusters in metalloproteins are known to be sensitive to molecular oxygen with dramatic consequences for their biological function. We performed a systematic quantum chemical investigation that sheds light on the differences in oxygen sensitivity depending on charge and spin states of these clusters as well as on their spatial fixation by the enzyme's scaffold. We find that significant structural distortions are required to bind O2 exothermically to [Fe2S2] and [Fe3S4] clusters, while only small conformational changes allow for the thermodynamically favorable coordination of molecular oxygen to [Fe4S4] cubanes and [Fe4S3] clusters.Dalton Transactions 05/2013; · 3.84 Impact Factor -
Article: Kinetic Modeling of Hydrogen Conversion at [Fe] Hydrogenase Active-Site Models.
[show abstract] [hide abstract]
ABSTRACT: By means of density functional theory we investigate the catalytic cycle of active-site model complexes of [Fe] hydrogenase and study how ligand substitutions in the first coordination sphere of the reactive Fe center affect the free-energy surface of the whole reaction pathway. Interestingly, dispersion interactions between the active site and the hydride acceptor MPT^⁺ render the hydride transfer step less endergonic and lower its barrier. Substitution of CO by CN^-, which resembles [FeFe] hydrogenase-like coordination, inverts the elementary steps H^- transfer and H_2 cleavage. A simplified kinetic model reveals the specifics of the interplay between active-site composition and catalysis. Apparently, the catalytic efficiency of [Fe] hydrogenase can be attributed to a flat energy profile throughout the catalytic cycle. Intermediates that are too stable, as they occur e.g. when one CO ligand is substituted by CN^-, significantly slow down the turnover rate of the enzyme. The catalytic activity of the wild-type form of the active-site model could, however, be enhanced by a PH_3 ligand substitution of the CO ligand.The Journal of Physical Chemistry B 04/2013; · 3.70 Impact Factor -
Article: Orbital entanglement in bond-formation processes
[show abstract] [hide abstract]
ABSTRACT: The accurate calculation of the (differential) correlation energy is central to the quantum chemical description of bond-formation and bond-dissociation processes. In order to estimate the quality of single- and multi-reference approaches for this purpose, various diagnostic tools have been developed. In this work, we elaborate on our previous observation [J. Phys. Chem. Lett. 3, 3129 (2012)] that one- and two-orbital-based entanglement measures provide quantitative means for the assessment and classification of electron correlation effects among molecular orbitals. The dissociation behavior of some prototypical diatomic molecules features all types of correlation effects relevant for chemical bonding. We demonstrate that our entanglement analysis is convenient to dissect these electron correlation effects and to provide a conceptual understanding of bond-forming and bond-breaking processes from the point of view of quantum information theory.03/2013; -
Article: An efficient implementation of two-component relativistic exact-decoupling methods for large molecules
[show abstract] [hide abstract]
ABSTRACT: We present an efficient algorithm for one- and two-component relativistic exact-decoupling calculations. Spin-orbit coupling is thus taken into account for the evaluation of relativistically transformed (one-electron) Hamiltonian. As the relativistic decoupling transformation has to be evaluated with primitive functions, the construction of the relativistic one-electron Hamiltonian becomes the bottleneck of the whole calculation for large molecules. For the established exact-decoupling protocols, a minimal matrix operation count is established and discussed in detail. Furthermore, we apply our recently developed local DLU scheme [J. Chem. Phys. 136 (2012) 244108] to accelerate this step. With our new implementation two-component relativistic density functional calculations can be performed invoking the resolution-of-identity density-fitting approximation and (Abelian as well as non-Abelian) point group symmetry to accelerate both the exact-decoupling and the two-electron part. The capability of our implementation is illustrated at the example of silver clusters with up to 309 atoms, for which the cohesive energy is calculated and extrapolated to the bulk.03/2013; -
Article: Optimized unrestricted Kohn–Sham potentials from ab initio spin densities
[show abstract] [hide abstract]
ABSTRACT: The reconstruction of the exchange–correlation potential from accurate ab initio electron densities can provide insights into the limitations of the currently available approximate functionals and provide guidance for devising improved approximations for density-functional theory (DFT). For open-shell systems, the spin density is introduced as an additional fundamental variable in spin-DFT. Here, we consider the reconstruction of the corresponding unrestricted Kohn–Sham (KS) potentials from accurate ab initio spin densities. In particular, we investigate whether it is possible to reconstruct the spin exchange–correlation potential, which determines the spin density in unrestricted KS-DFT, despite the numerical difficulties inherent to the optimization of potentials with finite orbital basis sets. We find that the recently developed scheme for unambiguously singling out an optimal optimized potential [Ch. R. Jacob, J. Chem. Phys. 135, 244102 (2011)10.1063/1.3670414] can provide such spin potentials accurately. This is demonstrated for two test cases, the lithium atom and the dioxygen molecule, and target (spin) densities from full configuration interaction and complete active space self-consistent field calculations, respectively.The Journal of Chemical Physics 01/2013; 138:044111. · 3.33 Impact Factor
