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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 5001-5002 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 108 (1986), S. 5708-5711 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 106 (1984), S. 4049-4050 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 522-526 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We propose a simple and efficient method for calculating vibrational bound states of molecular systems. The technique is based upon iterative solution of the collocation equations. A localized basis set is used which is very efficient for strongly coupled modes and also leads to a diagonally dominant set of collocation equations. The iterative scheme developed is based upon Davidson's method and takes advantage of this diagonal dominance. The approach is capable of exploiting the efficiency with which the matrix elements are calculated in the collocation method by evaluating the matrix elements as they are required. This combination of techniques should allow the method to be used for systems which have more degrees of freedom than have been treated by conventional methods.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3504-3508 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An iterative method is proposed for calculating the S matrix in the Kohn variational approach. Instead of solving the system of linear equations directly, the method consists of a block Lanczos algorithm extended to complex symmetric matrices and a matrix continued fraction procedure. Applications to inelastic and reactive scattering calculations indicate a reasonable rate of convergence.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6598-6603 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method is presented for calculating energy levels of atom–rigid-diatom systems for various values of the total angular momentum (J) of the complex. The technique is based upon the collocation method for the vibrational motions of the system and the Galerkin approach for the total rotation. Unlike the Rayleigh–Ritz variational principle, the method does not require the evaluation of integrals over the Hamiltonian and so is very simple to implement. An important feature of the method is that the wave function is obtained in an analytic form and so it is a simple matter to calculate many quantities of spectroscopic interest such as rotational constants and spectral intensities. It is also shown that contracted basis sets can be used in conjunction with the collocation method to enhance the efficiency of the calculation. The method is demonstrated by calculating rovibrational levels of the van der Waals complex Ar–HCl for J up to 10.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1208-1214 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A local projection method is proposed for obtaining the solution of the Kohn–Sham equation within the density-functional theory of molecules. The method uses the conventional linear combination of atomic orbitals as the approximate orbitals. However, it does not require multicenter integration in the construction of algebraic eigenvalue equations, and thus significantly reduces the corresponding computational effort. The method is tested on the self-consistent calculations of nitrogen molecules, N2, with basis sets of various accuracies and found to give results which are as accurate as the conventional approach. It is also shown that the local projection method can be applied to the non-self-consistent calculation scheme and provides a most efficient method for carrying out this type of electronic structure calculations.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7537-7542 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A collocation approach to quantum scattering is presented. The method is based on the S-matrix version of the Kohn variational principle with a different linear expansion used for the two wave functions—one is a linear combination of basis functions and the other is a pointwise representation with proper asymptotic conditions imposed. The resulting equations are similar in structure to the usual version of the Kohn variational principle, however, in the present approach there are no integrals between the square integrable (L2) basis functions. In addition, the method does not require the knowledge of quadrature weights associated with the collocation points as was the case in a previous pointwise method for quantum scattering. This property means that the method is readily applicable to reactive scattering problems which use different sets of coordinates for reactants and products. Appliction to a simple inelastic test problem (collinear He–H2 vibrationally inelastic scattering) shows the accuracy of the approach to be comparable to that of the usual variatinal form of the S-matrix Kohn method.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1746-1751 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ability of the collocation method to calculate vibrational bound states of molecules is investigated. The technique is simpler to implement than conventional variational methods; no integration over the basis functions is involved. We apply the method to the weakly bound complex Ar–HCl, a real multidimensional system of considerable physical interest, and find the procedure to be of equivalent accuracy to the corresponding variational approach at all times. This confirms the conclusions of our previous studies on one-dimensional test problems [W. Yang and A. C. Peet, Chem. Phys. Lett. (in press)]. Both low lying and highly excited states are examined and the conclusions hold even for levels very close to the dissociation limit. A test of the wave functions obtained also finds these to be of good accuracy and very similar to the ones given by the variational procedure.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 2334-2336 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: As previously shown [M. Levy and J. P. Perdew, Phys. Rev. A (in press)], the customary Hohenberg–Kohn density functional, based on the universal functional F[ ρ], does not exhibit naively expected scaling properties. Namely, if ρλ=λ3ρ(λr) is the scaled density corresponding to ρ(r), the expected scaling, not satisfied, is T[ρλ]=λ2T[ρ] and V[ρλ]=λV[ρ], where T and V are the kinetic and potential energy components. By defining a new functional of ρ and λ, F[ ρ, λ], it is now shown how the naive scaling can be preserved. The definition is F[ρ(r), λ]=〈λ3N/2 Φminρλ (λr1... λrN)|Tˆ(r1...rN) +Vee(r1...rN)| λ3N/2Φminρλ(λr1...λrN)〉, where λ3N/2 Φminρλ(λr1... λrN) is that antisymmetric function Φ which yields ρλ(r)=λ3ρ(λr) and simultaneously minimizes 〈Φ|Tˆ(r1...rN) +λVee(r1...rN)|Φ〉. The corresponding variational principle is EvG.S.=Infλ, ρ(r){∫ drv(r) ρλ(r)+λ2T[ ρ(r)] +λVee[ ρ(r)]}, where EvG.S. is the ground-state energy for potential v(r). One is thus allowed to satisfy the virial theorem by optimum scaling just as if the naive scaling relations were correct for F[ ρ].
    Type of Medium: Electronic Resource
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