Publications (13) View all
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Article: A kinetic energy fitting metric for resolution of the identity second-order Møller-Plesset perturbation theory.
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ABSTRACT: A kinetic-energy-based fitting metric for application in the context of resolution of the identity second-order Møller-Plesset perturbation theory is presented, which is derived from the Poisson equation. Preliminary tests of the applicability include the evaluation of the error in the correlation energy, compared to standard Møller-Plesset perturbation theory, with respect to the auxiliary basis set employed. We comment on the potential merits of this fitting metric, compared to standard resolution of the identity second-order Møller-Plesset perturbation theory, and discuss its scaling behavior in the limit of large molecules.The Journal of Physical Chemistry A 03/2011; 115(13):2794-801. · 2.95 Impact Factor -
Article: Fast Sparse Cholesky Decomposition and Inversion using Nested Dissection Matrix Reordering
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ABSTRACT: Here we present an efficient, yet nonlinear scaling, algorithm for the computation of Cholesky factors of sparse symmetric positive definite matrices and their inverses. The key feature of this implementation is the separation of the task into an algebraic and a numeric part. The algebraic part of the algorithm attempts to find a reordering of the rows and columns which preserves at least some degree of sparsity and afterward determines the exact nonzero structure of both the Cholesky factor and its corresponding inverse. It is based on graph theory and does not involve any kind of numerical thresholding. This preprocessing then allows for a very efficient implementation of the numerical factorization step. Furthermore this approach even allows use of highly optimized dense linear algebra kernels which leads to yet another performance boost. We will show some illustrative timings of our sparse code and compare it to the standard library implementation and a recent sparse implementation using thresholding. We conclude with some comments on how to deal with positive semidefinite matrices.01/2011; -
Article: Preparation of imidazolin-2-iminato molybdenum and tungsten benzylidyne complexes: a new pathway to highly active alkyne metathesis catalysts.
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ABSTRACT: The reaction of [PhC[triple bond]MBr(3)(dme)] (dme=1,2-dimethoxyethane) with the hexafluoro-tert-butoxides LiX or KX [X=OC(CF(3))(2)Me] afforded the benzylidyne complexes [PhC[triple bond]MX(3)(dme)] (2a: M=W, 2b: M=Mo), which further reacted with the lithium reagent Li(Im(tBu)N), generated with MeLi from 1,3-di-tert-butylimidazolin-2-imine (Im(tBu)NH), to form the imidazolin-2-iminato complexes [PhC[triple bond]MX(2)(Im(tBu)N)] (3a: M=W, 3b: M=Mo). The propylidyne complex [EtC[triple bond]MoX(2)(NIm(tBu))] (4) was obtained by treatment of 3b with an excess of 3-hexyne. Complexes 3a and 3b are able to efficiently catalyse alkyne cross metathesis of various 3-pentynyl benzyl ethers 5 and benzoic esters 7 at room temperature, to afford 2-butyne and the corresponding diethers 6 and diesters 8. The tungsten complex 3a proved to be a superior catalyst for ring-closing alkyne metathesis, and the [10]cyclophanes 10 and 12 were synthesised in high yield from 1,3-bis(3-pentynyloxymethyl)benzene (9) and bis(3-pentynyl) phthalate (11), respectively. The molecular structures of compounds 2a, 2b, 3a, 3b, 4, and 12 were determined by single-crystal X-ray diffraction. DFT calculations have been carried out for catalyst systems based on the imidazolin-2-iminato tungsten and molybdenum complexes 3a and 3b by choosing the alkyne metathesis of 2-butyne as the model reaction; the studies revealed a lower activation barrier for the tungsten system.Chemistry 08/2010; 16(29):8868-77. · 5.93 Impact Factor -
Article: Efficient computation of compliance matrices in redundant internal coordinates from Cartesian Hessians for nonstationary points
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ABSTRACT: We present an extension to the theory of compliance matrices, which is valid for arbitrary nonstationary points on the potential energy hypersurface. It is shown that compliance matrices computed as the inverse of the covariant Hessian matrix obey the same invariance properties with respect to different internal coordinate systems as they do for stationary points. Furthermore, we demonstrate how the computation of compliance matrices in arbitrary sets of redundant internal coordinates starting from a Cartesian Hessian can be achieved efficiently, and we discuss their potential usefullness in geometry optimization processesThe Journal of Chemical Physics 05/2010; 132(18):184101-184101-7. · 3.33 Impact Factor -
Article: Experimental and Theoretical Investigations of Catalytic Alkyne Cross-Metathesis with Imidazolin-2-iminato Tungsten Alkylidyne Complexes
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ABSTRACT: The imidazolin-2-iminato tungsten alkylidyne complexes [Me3CC≡W(NImR)(OR′)2] (4a: R = tBu, R′ = CMe3; 4b: R = Dipp, R′ = CMe3; 5a: R = tBu, R′ = CMe(CF3)2; 5b: R = Dipp, R′ = CMe(CF3)2 have been prepared from [Me3CC≡W(OCMe3)3] (2) and [Me3CC≡W{OCMe(CF3)2}3(dme)] (3, dme = 1,2-dimethoxyethane) by reaction with the lithium reagents Li(NImtBu) and Li(NImDipp), generated with MeLi from 1,3-di-tert-butylimidazolin-2-imine (ImtBuNH) or 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine (ImDippNH), respectively. Reaction of 3 with Li[N(tBu)Ar]·OEt2 (Ar = 3,5-dimethylphenyl) afforded the amido complex [Me3CC≡W{N(tBu)Ar}{OCMe(CF3)2}2] (6). Addition of Li[OCPh(CF3)2] to [Me3CC≡WCl3(dme)] (1) produced the dme-free complex [Me3CC≡W{OCPh(CF3)2}3] (7), which, upon treatment with Li(NImtBu), gave the alkylidene complex 8, presumably formed by activation and addition of an ortho-C−H bond across the W≡C bond in the intermediate alkylidyne complex. Treatment of 1 with Li[OC(CF3)3] led to the substitution of only two chloride ligands and formation of cis-[Me3CC≡WCl{OC(CF3)3}2(dme)] (9), which exhibits long-range through-space 19F−19F coupling between the fluorine atoms of the two OC(CF3)3 ligands. Reaction of 9 with Li(NImtBu) resulted in partial cleavage of the ImtBuN ligand and ligand redistribution to afford the dinuclear tungsten alkylidyne complex 10. The propylidyne complex [EtC≡W(NImtBu){OCMe(CF3)2}2] (12) was obtained by treatment of 5a with 3-hexyne, which proceeded via the metallacyclobutadiene complex 11. Complex 5a is able to rapidly catalyze alkyne cross-metathesis of 3-heptyne to give a statistical 1:2:1 mixture of 3-hexyne, 3-heptyne and 4-octyne. The catalytic homodimerization of 1-phenylpropyne under vacuum-driven conditions was studied for 5a, 5b and 6 at 30 and 80 °C. The molecular structures of complexes 2, 3, 4a, 4b, 5b, 8, 9, 10 and 12 were determined by single crystal X-ray diffraction. High-level DFT calculations employing the B3LYP functional have been carried out for a series of experimentally studied and other alkylidyne complexes by choosing alkyne metathesis of 2-butyne as the model reaction.03/2009;
