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  • 1
    Electronic Resource
    Electronic Resource
    Møller–Plesset perturbation theory calculation of alkaline earth–rare gas complexes: Ground states of Mg–He and Mg–Ar (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1114-1120 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used Møller–Plesset perturbation theory as carried out through the fourth order for a determination of the potential parameters for the ground states of the alkaline–earth metal magnesium with argon and helium. Mg–He was found to have a potential minimum of (approximate)0.021 mhartree at an internuclear distance of 9.75 a0 and was determined to be capable of supporting a single vibrational level. Mg–Ar was found to have a potential minimum of (approximate)0.254 at an internuclear distance of 9 a0 , which is slightly shallower and at a larger internuclear distance than a recent experimental determination. A comparison of the homonuclear and heteronuclear bonding is presented and differences in the bonding are attributed to exchange–repulsion effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457630
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  • 2
    Electronic Resource
    Electronic Resource
    Møller–Plesset perturbation theory for van der Waals complexes bound by electron correlation effects: Ground states of the Ar and Mg dimers (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3569-3579 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We demonstrate that MPPT through fourth order is suitable for studying van der Waals correlation-bound complexes provided that (a) accurate calculations are carried at the SCF level; (b) efficient basis sets for intersystem correlation effects (i.e., dispersion) are used; and (c) the full counterpoise (CP) method is applied to correct for basis set superposition error (BSSE). Interaction potentials are obtained for Ar2 and Mg2 with extended basis sets that contained up through the f-symmetry functions. For Ar2 the potential is characterized by R(approximate)7.3 a0 and De∼0.34 mhartree and for Mg2 by Re(approximate)7.4a0 and De∼2.1 mhartree. The discrepancies between our potentials and the most accurate semiempirical and experimental results (Ar2:Re∼7.1a0, De (approximate)0.45 mhartree; Mg2:Re(approximate)7.35a0, De∼1.93 mhartree, are analyzed in detail and attributed to the lack of higher than f-symmetry functions, as well as, in the Mg2 case, to the approximate nature of the MP4 approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453002
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio potential-energy surface for the He(1S)+NO(X 2Π) interaction and bound rovibrational states (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 2195-2203 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Adiabatic potential-energy surfaces for the 2A′ and 2A″ states of the He(1S)–NO(X 2Π) complex have been calculated at the restricted coupled cluster level of theory including single, double, and noniterated triple excitations [RCCSD(T)]. The potential-energy surface (PES) of the A′ state has three minima: for the T-shaped geometry, barely skewed toward oxygen (R=6.07 a0, aitch-theta=96.7°, and De(approximate)29.2 cm−1), and for two collinear forms. In contrast, PES of the A″ state has two minima, both related to T-shaped forms: (i) A global minimum, with He shifted toward nitrogen (R=6.27 a0, aitch-theta=76.1°, and De(approximate)25.3 cm−1), and a shoulderlike minimum, with He shifted toward oxygen (R=6.34 a0, aitch-theta=117.6°, and De(approximate)24.5 cm−1). The collinear forms of the A″ state correspond to saddle points. The A′ surface lies above the A″ surface, except in the vicinity of perpendicular arrangement. The interaction energies have been analyzed via perturbation theory of intermolecular forces. The shape and location of the minima is determined primarily by the anisotropy of the exchange component, and stronger repulsion of A′ is due to repulsion between the singly occupied anti-bonding π* orbital and He. A variational calculation of the bound rovibrational states supported by the potential suggests that the HeNO complex is bound by about 7 cm−1. The bound levels correlate with NO rotational levels with j=1/2 and j=3/2, and are well described as nearly free-rotor states in which j (NO rotation) and L (end-over-end rotation of R) are nearly good quantum numbers. Excited intermolecular stretching vibrations are not predicted to be bound. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480785
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  • 4
    Electronic Resource
    Electronic Resource
    On the role of bond functions in interaction energy calculations: Ar⋅⋅⋅HCl, Ar⋅⋅⋅H2O, (HF)2 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 1498-1507 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We analyze the effect of an extended set of bond functions on the SCF and MP2 interaction energies, and their SAPT perturbation components; electrostatic, induction, dispersion, and exchange. The electrostatic, induction, and exchange terms at the SCF level prove to be largely independent. The dispersion energy is substantially improved and the improvement did not depend much on the bond-function location. In contrast, the electrostatic-correlation term is usually seriously distorted and the distortion strongly dependent on the bond-function location. It was also shown that the distortion may be significantly reduced by appropriate shifting of the location. Only then the interaction energies obtained with bond functions may be considered reliable. It is strongly recommended to control the electrostatic-correlation term. We also present samples of accurate results (within 5% error bar) for the Ar–HCl, Ar–H2O, and (HF)2 complexes. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469771
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  • 5
    Electronic Resource
    Electronic Resource
    Ab initio study of He(1S)+Cl2(X 1Σg,3Πu) potential energy surfaces (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6800-6809 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential energy surface of the ground state He+Cl2(1Σg) is calculated by using the perturbation theory of intermolecular forces and supermolecular Møller–Plesset perturbation theory approach. The potential energy surface of the first excited triplet He+Cl2(3Πu) was evaluated using the supermolecular unrestricted Møller–Plesset perturbation theory approach. In the ground state two stable isomers are found which correspond to the linear He–Cl–Cl structure (a primary minimum, De=45.1 cm−1, Re=4.25 A(ring)) and to the T-shaped structure with He perpendicular to the molecular axis (a secondary minimum, De=40.8 cm−1, Re=3.5 A(ring)). The small difference between these geometries is mainly due to the induction effect which is larger for the linear form. The results obtained for the T-shaped minimum are in good agreement with the excitation spectroscopy experiments which observed only the T-shaped form [Beneventi et al., J. Chem. Phys. 98, 178 (1993)]. In the lowest triplet states correlating with Cl2(3Πu), 3A' and 3A‘, the same two isomers correspond to minima. Now, however, the T-shaped form is lower in energy. The 3A' and 3A‘ states correspond to (De,Re) of (19.9 cm−1, 3.75 A(ring)) and (30.3 cm−1, 3.50 A(ring)), respectively, whereas the linear form is characterized by (19.8 cm−1, 5.0 A(ring)). The binding energy for the T form in the lower 3A‘ state is in good agreement with the experimental value of Beneventi et al.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468308
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  • 6
    Electronic Resource
    Electronic Resource
    Supermolecular approach to many-body dispersion interactions in weak van der Waals complexes: He, Ne, and Ar trimers (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 8860-8869 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using the diagrammatic many-body perturbation theory, various three-body dispersion terms that appear in the intermolecular Møller–Plesset perturbation theory (MPPT) are identified and classified with regard to the effects of intramonomer electron correlation on the dispersion term. Via the connection with the supermolecular MPPT, it is demonstrated how the leading dispersion nonadditivities arise within supermolecular calculations that employ MPPT or coupled cluster formalisms. The numerical calculations for He3, Ne3, and Ar3 in triangular geometries fully confirm theoretical predictions. The calculated values of dispersion nonadditivity clearly show that the coupled cluster theory with single, double, and noniterative triple excitations provides the proper framework for the efficient inclusion of the intramonomer correlation effects in dispersion nonadditivity. The convergence of the two-body and three-body terms is shown to be very similar if we compare the three-body terms of an order higher than the two-body terms. This pattern is used to provide the estimates of the total nonadditivities in the three trimers within a few percent accuracy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468078
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  • 7
    Electronic Resource
    Electronic Resource
    Many-body theory of intermolecular induction interactions (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4998-5010 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The second-order induction energy in the symmetry-adapted perturbation theory is expressed in terms of electron densities and polarization propagators at zero frequency of the isolated monomers. This expression is used to derive many-body perturbation series with respect to the Møller–Plesset type correlation potentials of the monomers. Two expansions are introduced—one based on the standard Møller–Plesset expansion of electron densities and polarization propagators, and the second accounting for the so-called response or orbital relaxation effects, i.e., for the perturbation induced modification of the monomer's Fock operators. Explicit orbital formulas for the leading perturbation corrections that correctly account for the response effects are derived through the second order in the correlation potential. Numerical results are presented for several representative van der Waals complexes—a rare gas atom and an ion Ar–Na+, Ar–Cl−, and He–F−; a polar molecule and an ion H2O–Na+ and H2O–Cl−; two polar molecules (H2O)2; and a rare gas atom and a polar molecule Ar–HCl and He–HCl. It is shown that in the above systems, the significance of the correlation part of the induction energy varies from a very important one in the complexes of rare gas atoms and ions to a practically negligible one in the complexes of rare gases with polar molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467218
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  • 8
    Electronic Resource
    Electronic Resource
    Partitioning of interaction energy in van der Waals complexes involving excited state species: The He(1S)+Cl2(B 3Πu) interaction (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 10116-10127 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The partitioning of interaction energy between a closed-shell and an open-shell system is proposed. This allows us to describe the unrestricted Møller–Plesset interaction energy as a sum of fundamental contributions: electrostatic, exchange, induction and dispersion. The supermolecular energies derived within unrestricted Møller–Plesset perturbation theory are analyzed in terms of perturbation theory of intermolecular forces. The latter has been generalized to allow for the description of monomer wave functions within the unrestricted Hartree–Fock approach. The method is applied to the potential energy surfaces for the first excited triplet states, 3A′ and 3A″, of the He+Cl2(3Πu) complex. The 3A′ and 3A″ potential energy surfaces have different shapes. The lower one, 3A′, has a single minimum for the T-shaped structure. The higher one, 3A″, has the global minimum for the T-shaped structure and the secondary minimum for a linear orientation. The calculated well depth for the 3A′ state is 31.1 cm−1 at the 3.75 A(ring) intersystem separation at the UMP2 level with extended basis set involving bond functions. The 3A″ well depth is approximately 2.3 cm−1 smaller at this level. This order is reversed by higher correlation effects. The angular and radial behaviors of the individual components of the 3A′ and 3A″ interaction energies are compared to reveal the different nature of interaction energies in both states. A comparison with the ground state reveals that the A″ state has a typical van der Waals character similar to that of the ground state. The A′ state, on the other hand, differs considerably from the ground state. The A′ and A″ states differ primarily in different role of the intramonomer correlation effects. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469913
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  • 9
    Electronic Resource
    Electronic Resource
    Ab initio study of the He(1S)+CH(X 2Π) interaction (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 9525-9535 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy surfaces for the 2A′ and 2A″ states of the He(1S)–CH(X 2Π) complex were calculated using supermolecular unrestricted Møller–Plesset perturbation theory and analyzed via the relevant perturbation theory of intermolecular forces. It has been found that the two states are distinctly different. The potential energy surface (PES) of the A″ state has only a single and relatively deep minimum of De≈335 μEh for the T-shaped geometry, at R=5.0 a0 and aitch-theta=100°. The position of this minimum is determined by the exchange repulsion which is substantially reduced at this geometry. The minimum is unusually deep for a complex of He, and it can be viewed as an example of an incipient chemical bond. In contrast, the A′ state's PES represents a typical van der Waals interaction which is characterized by two similarly deep minima. The shape and location of these minima are determined primarily by the anisotropy of the dispersion component. The first minimum occurs for the collinear He–C–H arrangement, at R≈7.5 a0, and aitch-theta=0°, and is 55 μEh deep. The second minimum has a troughlike form which joins the region between R=7.5 a0, aitch-theta=140° and R=8.0 a0, aitch-theta=180°. The lowest point is approximately 54 μEh deep and occurs at R=7.5 a0 and aitch-theta=140°. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472820
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  • 10
    Electronic Resource
    Electronic Resource
    Origins and modeling of many-body exchange effects in van der Waals clusters (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3301-3310 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We analyze the many-body exchange interactions in atomic and molecular clusters as they arise in the supermolecular SCF and MP2 approaches. A rigorous formal setting is provided by the symmetry-adapted perturbation theory. Particular emphasis is put on the decomposition into the single exchange (SE) and triple exchange (TE) terms, at the SCF and correlated levels. We also propose a novel approach, whereby selected SE nonadditive exchange terms are evaluated indirectly, as differences of the two-body SAPT corrections arising between the components of the trimer treated as a complex of a dimer and a monomer (pseudodimer approach). This provides additional insights into the nature of various nonadditive effects, an interpretation of supermolecular interaction energies, and may serve as a viable alternative for the calculation of some SE terms. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473078
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