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Digitale Medien

A combined density functional and intrinsic reaction coordinate study on the ground state energy surface of H2CO (1993)

Deng, Liqun ; Ziegler, Tom ; Fan, Liangyou

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 99 (1993), S. 3823-3835

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Approximate density functional theory (DFT) has been used to study four elementary processes on the singlet ground state energy surface of H2CO. The elementary steps include the elimination of H2 and CO from formaldehyde, the transformation of formaldehyde to trans-hydroxymethylene, the isomerization of trans-hydroxymethylene to cis-hydroxymethylene, and the 1,2 elimination of H2 from cis-hydroxymethylene. The DFT studies were based on the local density approximation (LDA) as well as a nonlocal self-consistent field (NL-SCF) extension in which Perdew's correlation correction and Becke's exchange correction were added to LDA. Fully optimized structures as well as harmonic vibrational frequencies have been evaluated for all of the stationary points corresponding to the reactants, products, and transition states for the four reactions within the LDA and NL-SCF approximations. The four reactions have in addition been studied by the intrinsic reaction coordinate (IRC) method in which stationary points on the potential energy surface are connected by a steepest energy path. It is concluded that the NL-SCF method affords as good an overall fit to experiment as the fourth-order Møller–Plesset single, double, triple, and quadruple excitations [MP4(SDTQ)]/6-31G**//MP2/6-31G* scheme for the S0 surface of H2CO. The DFT methods tend to afford energies for the stationary points which are too low compared to the separate species H2+CO, whereas the corresponding MP4 energies are too high. This is in particular the case for the local LDA method. We attribute this trend to a bias in favor of bond formation among the DFT methods. The reaction paths for LDA and NL-SCF were found to be very similar, and it is suggested that one might combine geometries evaluated by the less demanding LDA method with energies obtained by the more accurate and involved NL-SCF scheme.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.466129

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Digitale Medien

Rotational Barriers in Trimethylenemethane-Fe(CO)2L Complexes. A Density Functional Study (1994)

Branchadell, Vicenc ; Deng, Liqun ; Ziegler, Tom

s.l. : American Chemical Society

Organometallics 13 (1994), S. 3115-3119

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ISSN: 1520-6041

Quelle: ACS Legacy Archives

Thema: Chemie und Pharmazie

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1021/om00020a028

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Digitale Medien

Potential Energy Surfaces of the Gas-Phase SN2 Reactions X- + CH3X = XCH3 + X- (X = F, Cl, Br, I): A Comparative Study by Density Functional Theory and ab Initio Methods (1994)

Deng, Liqun ; Branchadell, Vicenc ; Ziegler, Tom

s.l. : American Chemical Society

Journal of the American Chemical Society 116 (1994), S. 10645-10656

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ISSN: 1520-5126

Quelle: ACS Legacy Archives

Thema: Chemie und Pharmazie

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1021/ja00102a034

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Digitale Medien

Combined Density Functional Theory and Intrinsic Reaction Coordinate Study on the Conrotatory Ring-Opening of Cyclobutene (1995)

Deng, Liqun ; Ziegler, Tom

s.l. : American Chemical Society

The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 612-618

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Quelle: ACS Legacy Archives

Thema: Chemie und Pharmazie , Physik

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1021/j100002a025

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Digitale Medien

General aspects of ethylene polymerization by d0 and d0f n transition metals (1999)

Margl, Peter ; Deng, Liqun ; Ziegler, Tom

Springer

Topics in catalysis 7 (1999), S. 187-208

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ISSN: 1572-9028

Schlagwort(e): density functional theory ; olefin polymerization ; migratory insertion ; olefin complexation ; β-hydrogen elimination ; β-hydrogen transfer

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie

Notizen: Abstract We present a generalized view of d0and d0f n metal complexes as olefin polymerization catalysts from computational studies of the {L}M–C2H5 (0,+,2+)-fragments (M = Sc(III), Y(III), La(III), Lu(III), Ti(IV), Zr(IV), Hf(IV), Ce(IV), Th(IV) and V(V); L = NH–(CH)2–NH2- {1}, N(BH2)–(CH)2–(BH2)N2- {2}, O–(CH)3–O- {3}, Cp2 2- {4}, NH–Si(H2)–C5H4 2- {5}, {(oxo)(O–(CH)3–O)}3- {6}, (NH2)2 2- {7}, (OH)2 2- {8}, (CH3)2 2- {9}, NH–(CH2)3–NH2- {10} and O–(CH2)3–O2- {11}).

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1023/A:1019176119849

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Digitale Medien

The determination of intrinsic reaction coordinates by density functional theory (1994)

Deng, Liqun ; Ziegler, Tom

New York, NY : Wiley-Blackwell

International Journal of Quantum Chemistry 52 (1994), S. 731-765

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ISSN: 0020-7608

Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The first implementation of the intrinsic reaction coordinate (IRC) method within the density functional theory (DFT) framework is presented. The implementation has been applied to four different types of chemical reactions represented by the isomerization process, HCN = HNC (A); the SN2 process, H- + CH4 = CH4 + H- (B); the exchange process, H· + HX = HX + H· (X = F,Cl) (C); and the elimination process, C2H5Cl = C2H4 + HCl (D). The present study presents for each process optimized structures and calculated harmonic vibrational frequencies for the reactant(s), the transition state, and the product(s) along with the IRC path connecting the stationary points. The calculations were carried out within the local density approximation (LDA) as well as the LDA/NL scheme where the LDA energy expression is augmented by Perdew's and Becke's nonlocal (NL) corrections. The LDA and LDA/NL results are compared with each other as well as the best available ab initio calculations and experimental data. For reaction (D), ab initio calculations based on MP2 geometries and MP4SDTQ energies have been added due to the lack of accurate published post-HF calculations on this process. A detailed discussion is provided on the efficiency of the IRC algorithms, the relative accuracy of the DFT and ab initio schemes, as well as the reaction mechanisms of the four reactions. It is concluded that the LDA/NL scheme affords the same accuracy as does the MP4 method. The post-HF methods seem to overestimate activation energies, whereas the corresponding LDA/NL estimates are too low. The LDA activation energies are even lower than the LDA/NL counterparts. The incorporation of the IRC method into the DFT framework provides a promising and reliable tool for probing the chemical reaction path on the potential energy surfaces, even for large-size systems. IRC calculations by ab initio methods of an accuracy similar to the LDA/NL scheme, such as the MP4 scheme, are not feasible. © John Wiley & Sons, Inc.

Zusätzliches Material: 15 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/qua.560520406

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