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  • 1
    Electronic Resource
    Electronic Resource
    The location of transition states: A comparison of Cartesian, Z-matrix, and natural internal coordinates (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 888-904 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A comparison is made between geometry optimization in Cartesian coordinates, in Z-matrix coordinates, and in natural internal coordinates for the location of transition states. In contrast to the situation with minima, where all three coordinate systems are of comparable efficiency if a reliable estimate of the Hessian matrix is available at the starting geometry, results for 25 different transition states covering a wide range of structural types demonstrate that in practice Z-matrix coordinates are generally superior. For Cartesian coordinates, the commonly used Hessian update schemes are unable to guarantee preservation of the necessary transition state eigenvalue structure, while current algorithms for generating natural internal coordinates may have difficulty handling the distorted geometries associated with transition states. The widely used Eigenvector Following (EF) algorithm is shown to be extremely efficient for optimizing transition states. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 5 Tab.
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Molecular energies and properties from density functional theory: Exploring basis set dependence of Kohn - Sham equation using several density functionals (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 775-795 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The performance of four commonly used density functionals (VWN, BLYP, BP91, and Becke's original three-parameter approximation to the adiabatic connection formula, referred to herein as the adiabatic connection method or ACM) was studied with a series of six Gaussian-type atomic basis sets [DZP, 6-31G**, DZVP, TZVP, TZ2P, and uncontracted aug-cc-pVTZ (UCC)]. The geometries and dipole moments of over 100 first-row and second-row molecules and reaction energies of over 300 chemical reactions involving such molecules were computed using each of the four density functionals in combination with each of the six basis sets. The results were compared to experimentally determined values. Based on overall mean absolute theory versus experiment errors, it was found that ACM is the best choice for predictions of both energies of reaction [overall mean absolute theory versus experiment error (MATvEE) of 4.7 kcal/mol with our most complete (UCC) basis set] and molecular geometries (overall MATvEE of 0.92 pm for bond distances and 0.88° for bond angles with the UCC basis set). For routine calculations with moderate basis sets (those of double-ζ type: DZP, 6-31G**, and DZVP) the DZVP basis set was, on average, the best choice. There were, however, examples of reactions where significantly larger basis sets were required to achieve reasonable accuracy (errors ≤ 5 kcal/mol). For dipole moments, ACM, BP91, and BLYP performed comparably (overall MATvEE of 0.071, 0.067, and 0.059 debye, respectively, with the UCC basis set). Basis sets that include additional polarization functions and diffuse functions were found to be important for accurate density functional theory predictions of dipole moments. © 1997 by John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Constrained optimization in delocalized internal coordinates (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1079-1095 
    Details
    ISSN: 0192-8651
    Keywords: geometry optimization ; constraints ; delocalized internal coordinates ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Using the recently introduced delocalized internal coordinates, in conjunction with the classical method of Lagrange multipliers, an algorithm for constrained optimization is presented in which the desired constraints do not have to be satisfied in the starting geometry. The method used is related to a previous algorithm by the same author for constrained optimization in Cartesian coordinates [J. Comput. Chem., 13, 240 (1992)], but is simpler and far more efficient. Any internal (distance or angle/torsion) constraint can be imposed between any atoms in the system whether or not the atoms involved are formally bonded. Imposed constraints can be satisfied exactly. © 1997 John Wiley & Sons, Inc. J Comput Chem 18:1079-1095, 1997
    Additional Material: 2 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Predicting the vibrational spectra of some simple fluorocarbons by direct scaling of primitive valence force constants (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 1187-1204 
    Details
    ISSN: 0192-8651
    Keywords: vibrational spectra ; SQM force fields ; fluorocarbons ; density functional theory ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Using the scaled quantum-mechanical (SQM) force field approach with direct scaling of individual primitive force constants, we derive optimal scaling factors by a least-squares fit to the experimentally observed fundamentals of some selected “simple” fluorocarbons. We use the derived scaling factors to predict the vibrational spectra of all possible fluoromethanes, fluoroethylenes, fluoroethanes, and monofluoropropenes, proposing a reassignment of some experimental fundamentals. Two separate sets of scaling factors are derived for both traditional Hartree-Fock (HF) calculations and density functional theory (DFT) calculations using the hybrid three-parameter B3-PW91 density functional. With the split-valence 6-31G(d) basis set, our scaling procedure gives an average error of less than 9 cm-1 in the scaled frequencies with the B3-PW91 functional. The average percentage error is around 1%. The HF results are not as good - the average error is 12.6 cm-1 - showing that hybrid density functional SQM schemes are better for predicting vibrational spectra than basic Hartree-Fock.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 1187-1204, 1998
    Additional Material: 2 Ill.
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  • 5
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    Effects of the obese gene product on body weight regulation in ob/ob mice (1995)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1995-07-28
    Description: C57BL/6J mice with a mutation in the obese (ob) gene are obese, diabetic, and exhibit reduced activity, metabolism, and body temperature. Daily intraperitoneal injection of these mice with recombinant OB protein lowered their body weight, percent body fat, food intake, and serum concentrations of glucose and insulin. In addition, metabolic rate, body temperature, and activity levels were increased by this treatment. None of these parameters was altered beyond the level observed in lean controls, suggesting that the OB protein normalized the metabolic status of the ob/ob mice. Lean animals injected with OB protein maintained a smaller weight loss throughout the 28-day study and showed no changes in any of the metabolic parameters. These data suggest that the OB protein regulates body weight and fat deposition through effects on metabolism and appetite.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pelleymounter, M A -- Cullen, M J -- Baker, M B -- Hecht, R -- Winters, D -- Boone, T -- Collins, F -- New York, N.Y. -- Science. 1995 Jul 28;269(5223):540-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Neurobiology, Amgen, Inc., Thousand Oaks, CA 91320, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/7624776" target="_blank"〉PubMed〈/a〉
    Keywords: Adipose Tissue/drug effects ; Analysis of Variance ; Animals ; Blood Glucose/analysis ; Body Composition/drug effects ; Body Temperature/drug effects ; Dose-Response Relationship, Drug ; Drinking/drug effects ; Eating/*drug effects ; Energy Metabolism/drug effects ; Female ; Insulin/blood ; Leptin ; Mice ; Mice, Inbred C57BL ; Mice, Obese ; Motor Activity/drug effects ; Obesity/genetics/*physiopathology ; Oxygen Consumption/drug effects ; Proteins/genetics/*pharmacology ; Recombinant Proteins/pharmacology ; Weight Loss/*drug effects
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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