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  • Articles  (14)
  • American Institute of Physics (AIP)  (14)
  • 1995-1999  (14)
  • Chemistry and Pharmacology  (14)
  • Political Science
  • Mathematics
  • 1
    Electronic Resource
    Electronic Resource
    Full configuration–interaction and state of the art correlation calculations on water in a valence double-zeta basis with polarization functions (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8007-8015 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a valence double-zeta polarization basis, full configuration–interaction (FCI) calculations are carried out on water at its equilibrium geometry and at geometries where the OH bond lengths are stretched until dissociation. At the same geometries and with the same basis set configuration interaction calculations at excitation levels up to hextuples, multireference singles doubles configuration interaction calculations, coupled cluster calculations at excitation levels up to quadruples, Møller–Plesset perturbation theory calculations through order fifteen, and complete active space second-order perturbation theory calculations are also carried out. The static correlation contribution increase with increasing bond length. The calculations show that the coupled cluster approach has a remarkable ability to describe even relatively large static correlation contributions. The single reference perturbation expansion breaks down for larger OH bond length, while the multireference approach preserves the accuracy for the whole potential curve. At the equilibrium geometry, FCI calculations have also been carried out for the lowest state of 2A1, 2B1, and 2B2 symmetry of H2O+, and the results compared with state of the art correlation results for total energies and ionization potentials (IP's). Differential energies (IP's) are obtained more accurately than absolute (total) energies in the size extensive coupled cluster and perturbation approaches. For the nonsize extensive configuration interaction method errors are obtained of the same size for differential and absolute energies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471518
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  • 2
    Electronic Resource
    Electronic Resource
    Direct subsurface absorption of hydrogen on Pd(111) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4330-4336 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We summarize and discuss some of the available experimental and theoretical data important for understanding the role played by subsurface sites in dissociative chemisorption calculations for the H2/Pd(111) system. Then we use a semi-empirical potential energy surface (PES) to model the interaction of a H2 molecule impinging on a Pd(111) surface. The London–Eyring–Polanyi–Sato (LEPS) construction has been extended to make direct subsurface absorption possible. A two-dimensional wave packet calculation is used to find qualitative trends in the direct subsurface absorption and to reveal the time scales involved. We suggest that a partial in-plane relaxation occurs for the slowest incoming particles, thus resulting in a higher direct subsurface absorption probability for low energies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471541
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  • 3
    Electronic Resource
    Electronic Resource
    A multiconfiguration self-consistent-field response study of one- and two-photon dipole transitions between the X 1Σ+ and A 1Π states of CO (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 4143-4150 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The one- and two-photon dipole transitions between the X 1Σ+ and the A 1Π states of CO have been studied by means of multiconfiguration self-consistent-field linear and quadratic response methods. The vibrationally averaged oscillator strength for the 0–0 one-photon dipole transition between the X 1Σ+ and A 1Π states obtained using the linear response method is 1.31×10−2 as compared to the experimental results of 0.96(14)×10−2, 1.08(7)×10−2, and 1.11×10−2. The two-photon transition probability rate constant, obtained using the quadratic response method, for the 0–1 vibrational band of the X–A transition of 7×10−59 cm4 s is more than six orders of magnitude smaller than the experimental result of 3.5×10−52 cm4 s. We suggest that the experiment should be reconsidered. The dipole moment of the A 1Π state obtained from quadratic response calculations on the ground state at R=2.332 a.u. is −0.0441 a.u. suggesting an anomalous polarity also for the A 1Π state. The experimental value is ±0.059(20) a.u. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468542
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  • 4
    Electronic Resource
    Electronic Resource
    Quasiperiodicity in a detailed model of the peroxidase–oxidase reaction (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 10849-10859 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quasiperiodicity in models of the peroxidase–oxidase reaction has previously been reported in "abstract'' or phenomenological models which sacrifice chemical realism for tractability. In the present paper, we discuss how such behavior can arise in a detailed model (BFSO) of the reaction which has previously been shown to be consistent with experimental findings. We distinguish two types of quasiperiodic behavior. Regions of what we here refer to as "primary'' quasiperiodicity are delimited by supercritical secondary Hopf bifurcations at one end of the relevant range of parameter values and by heteroclinic transitions at the other. Regions of so-called "secondary quasiperiodicity'' are delimited by supercritical Hopf bifurcations at both ends of the parameter range. The existence of a quasiperiodic route to chaos in a modified version of BFSO is also described. This paper emphasizes the experimental circumstances under which quasiperiodic dynamics may be detected in the lab and offers specific prescriptions for its observation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472927
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  • 5
    Electronic Resource
    Electronic Resource
    Surprising cases of divergent behavior in Møller–Plesset perturbation theory (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 5082-5090 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-order Møller–Plesset perturbation calculations have been carried out for several small molecules and compared to full configuration interaction (FCI) results. The convergence of the Møller–Plesset series is found to depend crucially on the one-electron basis sets. Addition of diffuse basis functions leads in some cases to divergent behavior of the Møller–Plesset series, even for highly single reference dominated systems as Ne and HF. The results thus questions the usefulness of higher-order perturbation calculations as a vehicle for obtaining arbitrary accuracy of quantum chemical calculations and raises the fundamental theoretical question: When does Møller–Plesset perturbation theory converge for many-electron systems in extended basis sets? © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472352
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  • 6
    Electronic Resource
    Electronic Resource
    Polarizabilities and first hyperpolarizabilities of HF, Ne, and BH from full configuration interaction and coupled cluster calculations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1917-1925 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Static and frequency-dependent polarizabilities and first hyperpolarizabilities have been calculated for HF and Ne using full configuration interaction (FCI) and a hierarchy of coupled cluster models: coupled cluster singles (CCS), an approximate coupled cluster singles and doubles model (CC2), coupled cluster singles and doubles (CCSD), an approximate coupled cluster singles, doubles, and triples model (CC3), and coupled cluster singles, doubles, and triples (CCSDT). A previous study of BH concerning FCI benchmarking has been extended to include CC3 and static CCSDT values. Systematic improvements of the polarizabilities and the hyperpolarizabilities are found going from CCS to CCSD and from CCSD to CC3 or CCSDT. Little or no improvement of the polarizabilities and no improvement of the hyperpolarizabilities are seen when going from CCS to CC2. The CCSD results represent a significant improvement over CCS and CC2 but are again surpassed by the CC3 results which agree very well with the FCI values. The relative error for the static polarizability at the CC3 level is 0.11% for Ne and, respectively, 0.16% and 0.20% for αxx and αzz of HF. For βzzz and βzxx the errors are 0.50% and 1.7%, respectively. Only in the challenging case of BH does CCSDT improve the CC3 values. The dispersion for the polarizabilities and hyperpolarizabilities is predicted with increasing accuracy in the CCS–CC2–CCSD–CC3 sequence as expected from the increasing accuracy of the electronic excitation energies. For all molecules the effect of orbital relaxation has been investigated for the static properties. The inclusion of orbital relaxation gives results that are somewhat different from the unrelaxed results but are in general no improvement. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479460
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  • 7
    Electronic Resource
    Electronic Resource
    Atomic and molecular hydrogen interacting with Pt(111) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 11155-11163 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This computational study is motivated by the apparent conflict between an experiment on dissociation of H2 and D2 on Pt(111), which suggests a rather corrugated potential energy surface (PES) for the H2/Pt(111) system, and an experiment showing only weak nonzero-order diffraction of HD scattering from Pt(111). In the calculations we have used density functional theory (DFT) within the generalized gradient approximation (GGA), including scalar relativistic effects and modelling the Pt(111) surface as a slab. We have found that the H2/Pt(111) PES is both energetically and geometrically corrugated. We have also found that there are reaction paths without or with very low barriers leading to dissociation of H2 on the Pt(111) surface, but that there are other reaction paths with substantial barriers. By performing extensive calculations on H interacting with a Pt(111) surface we have shown that a DFT/GGA approach that includes scalar relativistic effects is capable of describing the interaction between a hydrogen atom and a Pt(111) surface in a way that is, for the most part, consistent with experiments. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480473
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of intermolecular interactions on the electric properties of helium and argon. I. Ab initio calculation of the interaction induced polarizability and hyperpolarizability in He2 and Ar2 (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10099-10107 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The frequency-dependent interaction induced polarizabilities and second hyperpolarizabilities are calculated for He2 at the coupled cluster singles and doubles and full configuration interaction levels and for Ar2 at the coupled cluster singles and doubles level. The frequency-dependence is approximated by a power series to second-order in the frequency arguments using Cauchy moments and hyperpolarizability dispersion coefficients. Using large correlation consistent basis sets, results close to the basis set limit are obtained. The computed curves for the interaction induced (hyper-) polarizabilities are tabulated for a range of internuclear distances. The data are employed in a companion paper to make for the first time a direct comparison between the experimentally determined pressure dependence of an ESHG hyperpolarizability and ab initio calculated hyperpolarizability second virial coefficients. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480361
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  • 9
    Electronic Resource
    Electronic Resource
    Full configuration interaction benchmark calculations of first-order one-electron properties of BH and HF (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 734-740 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Full configuration interaction benchmark calculations have been carried out for the electric dipole and quadrupole moments and the electric field gradient at the nuclei of BH and HF. The accuracy of perturbation theory from second to fourth order and coupled cluster theory with up to triple excitations has been investigated. For all the properties the coupled cluster models outperform the perturbation series. The convergence of the series of coupled cluster models is significantly faster and more systematic than the one of the perturbation series, and only the coupled cluster series defines a hierarchy of models with well defined levels of accuracy. The CCSD(T) model is a good approximation to the full coupled cluster singles, doubles, and triples model. It recovers 80%–90% of the full effect of triple excitations, and the small error due to the approximate description of triple excitations is comparable in size to the error due to neglect of higher-order excitations. For accurate calculations, the CCSD(T) model is the preferred model for all the properties. Our estimates of the exact dipole moments μe(HF)=1.802±0.003 D and μ0(BH)=1.356±0.004 D are in perfect agreement with the experimental values of μe(HF)=1.803±0.002 D and μ0(BH)=1.27±0.21 D. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478042
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  • 10
    Electronic Resource
    Electronic Resource
    The influence of molecular rotation on the direct subsurface absorption of H2 on Pd(111) (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 2450-2459 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Within the generalized gradient approximation (GGA) of density functional theory (DFT) we have calculated a three-dimensional (3D) potential energy surface (PES) including an angular degree of freedom for a H2 molecule interacting with a Pd(111) surface. There is an entrance channel barrier ((approximate)0.09 eV) to both dissociative chemisorption and direct subsurface absorption, but after this barrier is crossed direct subsurface absorption can proceed almost without a barrier. 3D quantum mechanical wave packet calculations incorporating the rotation of H2 in a plane perpendicular to the surface show a large part of the hydrogen going directly subsurface even at low incident kinetic energies. The wave packet calculations also show that in the low energy regime rotation inhibits direct subsurface absorption at low j0 and promotes it at high j0. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476815
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