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ABSTRACT: Based on the integrated molecular orbital and molecular mechanics approach, we constructed a combined quantum mechanics (QM) and molecular mechanics (MM) method, by combining the parallel density functional program ParaGauss with the MM3 force field. We examined different ways to describe link atoms at the boundary between the QM and MM regions which we tested successfully on various organic molecules. We applied the new tool, intended for the description of metal–ligand interaction, to model Cu thiolate clusters. Separation at the first C–C bond was favored over a transition at the S–C bond, closer to the metal particle. We successfully checked the effect of different ligand orientations on the cluster geometry by comparison with QM calculations. Hybrid calculations correctly described geometric rearrangements to avoid steric stress of larger ligands. Thus, the QM/MM approach is also applicable when direct metal–metal interactions have to be treated.
Theoretical Chemistry Accounts 06/2003; 109(6):285-297. · 2.16 Impact Factor
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ABSTRACT: A c(2×2) sulfur overlayer on Ni(110), produced by adsorption and thermal dissociation of H2S has been investigated with vibrational electron energy loss spectroscopy (EELS) and a feature at 331 cm−1 is assigned as a nickel-sulfur stretch. Also, cluster models of sulfur adsorption at Ni(001), Ni(110) and Ni(111) have been studied using the linear combination of Gaussian-type orbitals local density functional (LCGTO-LDF) method. The equilibrium bond distances and the absorbate vibrational stretching frequencies are found to be in good agreement with experiment, confirming the experimental assignment of the Ni(110)/S vibrational data.
Surface Science.
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ABSTRACT: Basic theoretical aspects of relativistic density functional theory as well as methodological details and key applications of the relativistic variant of the linear combination of Gaussian-type orbitals density functional (RLCGTO-DF) method are presented. Starting from the quantum electrodynamical Hamiltonian, an overview over relativistic density functional theory is given. The adaption of the second-order Douglas-Kroll-Hess scheme for solving the Dirac-Kohn-Sham equations results in a computationally efficient and numerically stable two-component Kohn-Sham formalism which is well suited for molecular applications, in particular due to the availability of analytical energy gradients. Finally, various applications of the RLCGTO-DF method to metal clusters to metal-ligand interactions, and to metal complex reactions are reviewed.
Theoretical and Computational Chemistry. 4:497-566.
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ABSTRACT: We present a class of exactly solvable quantum spin models which consist of two Heisenberg-subsystems coupled via a long-range Lieb-Mattis interaction. The total system is exactly solvable whenever the individual subsystems are solvable and allows the effects of frustration to be studied. We discuss the properties of two coupled antiferromagnetic chains and two coupled Lieb-Mattis antiferromagnets.
Physica B: Condensed Matter.
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ABSTRACT: Core eigenvalue spectra of naked and embedded cluster models of the Li (100) surface are compared to each other and to the core level energies of a five-layer 2D-periodic slab model. The electronic structure calculations have been carried out in the frame work of density functional theory, cluster embedding was performed by means of the moderately large embedded cluster scheme. The results for naked clusters reflect the inhomogeneous environment of the atoms due to artificial model boundaries. On the other hand, embedding yields discrete spectra that exhibit a close similarity to the energetic distribution of the slab core energies.
Chemical Physics Letters.
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ABSTRACT: We present grain-size distributions of the terrigenous fraction of two sediment cores from the southeast Levantine Sea (SL112) and the northern Aegean Sea (SL148), spanning the time interval from the late glacial to the present. End-member modelling of the grain-size distribution allows discriminating between aeolian and fluvial transport of the sediments and helps to infer palaeoenvironmental conditions in the source areas. Sedimentary and depositional processes during the late glacial and Holocene were controlled by climatic variations of both the northern high latitudes and the African climate system. The sedimentation at site SL112 off Israel is dominated by the suspension load of the River Nile and aeolian dust from the Sahara. Variations in grain size reflect the early to mid-Holocene climate transition from the African Humid Period to recent arid conditions. This climate change was gradual, in contrast to the abrupt humidity change documented in Western Saharan records. This implies a successive decrease in Nile river sediment supply due to a step-wise aridification of the headwaters. The grain-size data of SL112 show a humidity maximum at 5 kyr BP coincident with a regionally-restricted wet phase in the Levantine Sea. The sediments at the North Aegean site SL148 consist of riverine particles and low amounts of aeolian dust, probably derived from South European sources and with probably minor Saharan influence. The sedimentation processes are controlled by climate conditions being characterized by enhanced deposition of dust during the cold and dry glacial period and by decreased aeolian influx during the temperate and humid Holocene.
Marine Geology.
