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  • 1
    Electronic Resource
    Electronic Resource
    Towards multireference equivalents of the G2 and G3 methods (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 8758-8772 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of replacing the standard single-determinant reference wave functions in variants of G2 and G3 theory by multireference (MR) wave functions based on a full-valence complete active space has been investigated. Twelve methods of this type have been introduced and comparisons, based on a slightly reduced G2-1 test set, are made both internally and with the equivalent single-reference methods. We use CASPT2 as the standard MR-MP2 method and MRCl+Q as the higher correlation procedure in these calculations. We find that MR-G2(MP2,SVP), MR-G2(MP2), and MR-G3(MP2) perform comparably with their single-reference analogs, G2(MP2,SVP), G2(MP2), and G3(MP2), with mean absolute deviations (MADs) from the experimental data of 1.41, 1.54, and 1.23 kcal mol−1, compared with 1.60, 1.59, and 1.19 kcal mol−1, respectively. The additivity assumptions in the MR-Gn methods have been tested by carrying out MR-G2/MRCI+Q and MR-G3/MRCI+Q calculations, which correspond to large-basis-set MRCI+Q+ZPVE+HLC calculations. These give MADs of 1.84 and 1.58 kcal mol−1, respectively, i.e., the agreement with experiment is somewhat worse than that obtained with the MR-G2(MP2) and MR-G3(MP2) methods. In a third series of calculations, we have examined pure MP2 and MR-MP2 analogs of the G2 and G3 procedures by carrying out large-basis-set MP2 and CASPT2(+ZPVE+HLC) calculations. The resultant methods, which we denote G2/MP2, G3/MP2, MR-G2/MP2, and MR-G3/MP2, give MADs of 4.19, 3.36, 2.01, and 1.66 kcal mol−1, respectively. Finally, we have examined the effect of using MCQDPT2 in place of CASPT2 in five of our MR-Gn procedures, and find that there is a small but consistent deterioration in performance. Our calculations suggest that the MR-G3(MP2) and MR-G3/MP2 procedures may be useful in situations where a multireference approach is desirable. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1411998
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  • 2
    Electronic Resource
    Electronic Resource
    On the correlation energy features in planar heteroatomic molecular systems (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 3474-3483 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The correlation energy in planar heteroatomic open chain polyene systems involving N, O, and F atoms is considered by the CASSCF and CASPT2 methods employing a number of the cc-pVmZ (VDZ, VTZ, etc.) correlation consistent basis sets. A thorough study of the smallest molecules shows that the nondynamical correlation energy is virtually independent of the quality of the basis set. In contrast, the dynamical correlation energy is very sensitive to the basis set and, in estimating reliable dynamical correlation effects for larger systems, one has to rely on adequate extrapolation formulas to obtain the infinite basis set limit. We find that a method recently proposed by Truhlar offers economical yet reasonable estimates of the complete basis set results. Investigation of the sensitivity of the results to the choice of active space and the comparison to single reference MP2 calculations indicate that such extrapolations offer a good general method for saturating the basis set in multireference calculations. Thus a simple refinement of the conventional multireference coupled cluster method is proposed. It is also shown that both nondynamical and dynamical correlation energies follow very simple additivity rules in linear and branched planar chain heteroatomic polyenes, making possible their prediction in very large systems without calculation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1389290
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  • 3
    Electronic Resource
    Electronic Resource
    RACE-SPACE INEQUALITY IN SOUTH AFRICA: A STUDY IN WELFARE GEOGRAPHY (1974)
    Oxford, UK : Blackwell Publishing Ltd
    Antipode 6 (1974), S. 0 
    Details
    ISSN: 1467-8330
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geography
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1467-8330.1974.tb00595.x
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of Dietary Phospholipids on Digestion of Neutral Lipid by the Prawn Penaeus monodon (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the World Aquaculture Society 29 (1998), S. 0 
    Details
    ISSN: 1749-7345
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract— Different amounts of dietary phospholipid were tested for their effect on the digestibility of total neutral lipids in the diet of the prawn Penaeus monodon. A purified source of the phospholipid, L-α-phosphatidylcholine, was included at 0. 5, 10, 20 or 40 g/kg in a purified diet containing 80 g/kg olive oil as the predominant neutral lipid source. The apparent digestibility of the neutral lipid (ADNL) in these diets was determined by comparing concentrations of the digestibility marker, cholestane in the feed and faeces of the prawns. ADNL (%) increased curvilinearly with increasing dietary phospholipid content (X, %) as described by the equation: ADNL = 80.4 + 9.08X -1.705X2 (P 〈 0.05; R2= 0.71); the asymptote of 92.5% was achieved with a phosphatidylcholine value of 27 g/kg. These results demonstrate that phosphatidylcholine significantly increases the digestibility of neutral lipids by penaeid prawns. However, olive oil was used as the predominant neutral lipid source to examine the effects with a relatively poorly digestible lipid source. The effects of phosphatidylcholine on more readily digested lipid sources such as fish oils, may not be as great, but still be sufficient to improve the utilisation of these nutrients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-7345.1998.tb00660.x
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  • 5
    Electronic Resource
    Electronic Resource
    The C˜←X˜ transition in Ar⋅NO, Kr⋅NO, and Xe⋅NO studied using resonance-enhanced multiphoton ionization spectroscopy (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 4361-4366 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The C˜ 2Π(vNO′=0)←X˜ 2Π(v″=0) transitions in Ar⋅NO and Kr⋅NO are investigated using (2+1) resonance-enhanced multiphoton ionization (REMPI) spectroscopy. The spectra consist of vibrational progressions, each member of which is seen to have a reproducible pattern of much closer spaced features; the latter are assigned as rotational structure associated with the a inertial axis of a near T-shaped complex. The spectra are successfully simulated using this model, which yields information on the geometry of the molecular complex in these vibronic states. Comparison is made with previously reported spectra for the C˜ 2Π(vNO′=1 and 2)←X˜ 2Π(vNO″=0) transition. The corresponding spectrum for Xe⋅NO is also discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477038
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  • 6
    Electronic Resource
    Electronic Resource
    The A˜ 2Σ+ state of Ar⋅NO studied using resonance-enhanced multiphoton and zero-kinetic-energy pulsed-field ionization spectroscopy (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 406-415 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy pulsed-field ionization (ZEKE-PFI) techniques have been used to study the spectroscopy of the A˜ 2Σ+ state of Ar⋅NO. A˜ 2Σ+–X˜ 2Π REMPI spectra of Ar⋅NO have been interpreted using two different models that have allowed assignment of the observed rovibronic transitions to be made and an estimate of the strength of the A˜ state intermolecular potential to be determined. Simulations of the spectra have indicated that the ground vibrationless level of the A˜ state has a linear geometry while some higher vibrational levels have a skewed T-shaped structure. The analysis has also confirmed that the A˜ state of Ar⋅NO is very weakly bound and is non-Rydberg in character. Reported for the first time are ZEKE-PFI spectra observed via the intermediate A˜ 2Σ+ state. No structure was detected close to the ionization threshold, although peaks observed at higher excitation energy have been assigned to transitions to high-lying vibrational levels of the Ar⋅NO+ ion. ZEKE-PFI spectra recorded via the ground vibrational level of the intermediate A˜ state, which has a linear structure, show progressions which correlate with transitions to highly excited van der Waals stretching and bending levels; however, spectra recorded via an intermediate level with a T-shaped geometry show progressions which correlate principally with the van der Waals stretching mode. These assignments have been interpreted in terms of the large changes in intermolecular bond length and bond angle upon ionization and fully support the interpretation of the REMPI spectra. The results of the REMPI and ZEKE-PFI spectra have also been used to investigate the character of the A˜ state and the geometry that the complex adopts in each of the vibronic levels of this state has been rationalized in terms of the possible interactions involved.© 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475402
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  • 7
    Electronic Resource
    Electronic Resource
    An assessment of theoretical procedures for the calculation of reliable free radical thermochemistry: A recommended new procedure (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 604-615 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ability to predict reliable thermochemical properties of molecules and ions has led to an ever increasing application of ab initio molecular orbital theory. Methods such as G2 theory have been shown to generally give accurate heats of formation (ΔfH) for closed-shell molecules and ions. Open-shell systems have been less thoroughly examined to date and the present paper attempts to redress this situation through a detailed assessment of the performance of a variety of levels of theory in calculating ΔfH values for free radicals. Representatives of three families of theoretical procedures have been studied: the infinite basis set extrapolation techniques of Martin, the CBS procedures of Petersson et al., and the G2 methods of Pople et al. Among the specific influences investigated are choice of geometry, zero-point vibrational energy, high level electron correlation treatment and basis set size. We recommend a new procedure called CBS-RAD for the treatment of free radicals. CBS-RAD is a modification of the CBS-Q method in which the geometry and zero-point energies are obtained at the QCISD/6-31G(d) level, and coupled-cluster theory is used in place of quadratic configuration interaction in single-point energy calculations. We find that for free radicals with low spin contamination G2 theory also performs adequately, but as 〈S2〉 increases the results of G2 calculations can become increasingly unsatisfactory. The recommended CBS-RAD procedure should yield more reliable results over a broader range of free radicals. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476256
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  • 8
    Electronic Resource
    Electronic Resource
    One- and two-color resonance-enhanced multiphoton ionization spectroscopy of the Kr⋅NO complex via the A˜ 2Σ+ state (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 9804-9811 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A structured spectrum of the A˜ state of the Kr⋅NO complex has been obtained for the first time, employing the techniques of one-color (1+1) and two-color (1+1′) resonance-enhanced multiphoton ionization spectroscopy. The T0 value of the A˜←X˜ transition is 44 201±1 cm−1, and the spectrum allows estimates to be made of the dissociation energies (D0) of both the X˜ and A˜ states of ∼110 cm−1. Of significance is that the spectrum appears in both the Kr⋅NO+ mass channel and (when high photon intensities are used) in the Kr+ mass channel. Non-Rydberg behavior of the A˜ states of Ar⋅NO and Kr⋅NO is noted. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472934
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  • 9
    Electronic Resource
    Electronic Resource
    Erratum: "An assessment of theoretical procedures for the calculation of reliable free radical thermochemistry: A recommended new procedure" [J. Chem. Phys. 108, 604 (1998)] (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9598-9598 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476372
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  • 10
    Electronic Resource
    Electronic Resource
    On Performing Geography (2001)
    Oxford, UK and Boston, USA : Blackwell Publishers Ltd
    Antipode 33 (2001), S. 0 
    Details
    ISSN: 1467-8330
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geography
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1467-8330.00171
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