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  • 1
    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 109 (1987), S. 579-580 
    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
    New York, NY : Wiley-Blackwell
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This is the first application of a rigorous, established multiple time-step method to ab initio molecular dynamics. The resulting algorithm is conceptually simple and easy to implement, but very effective. It translates the large mass differences present in ab initio molecular dynamics into substantial savings in computer time while retaining high accuracy. This transforms ab initio molecular dynamics from a desirable but prohibitively expensive possibility into a viable method, at least for short-time phenomena in small systems or for otherwise inaccessibly complicated potential energy surfaces. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 4
    ISSN: 0192-8651
    Keywords: Gaussian fits ; Prony's method ; pseudospectral methods ; electron correlation ; aliasing error ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We present a method of fitting arbitrary functions to linear combinations of Gaussians. In particular, we discuss an adaptation of Prony's method, or separation of exponentials, which allows us to automatically select appropriate exponents for these Gaussians. We then apply this technique to the selection of dealiasing sets for pseudospectral electron correlation methods. We show that it can successfully choose functions that generally improve the accuracy of pseudospectral correlation energies while reducing the size of the dealiasing set chosen.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 1300-1314, 1998
    Additional Material: 5 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 17 (1996), S. 1836-1847 
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Based on Banach's principle, we formally obtain possible choices for an error vector in the direct inversion in the iterative subspace (DIIS) method. These choices not only include all previously proposed error vectors, but also a new type of error vector which is computationally efficient and applicable to much wider range of problems. The error vector analysis also reveals a strong connection between DIIS and damping, thus adding to understanding of the reasons behind DIIS's effect on convergence. We illustrate our conclusions with several examples. © 1996 by John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 862-865 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of basis set and electron correlation on the singlet–triplet splitting (ΔEST) of CH2 is examined using the generalized valence bond (GVB) approach. For a standard double zeta plus polarization basis, the GVB based calculation (with only 20–25 spin eigenfunctions) approaches the full CI result (∼220 000 spin eigenfunctions) of Bauschlicher and Taylor to within 0.5 kcal/mol for this basis, but both differ substantially from experiment (errors of 2.4 and 2.9 kcal/mol for GVB and full CI, respectively). We have studied the convergence of ΔEST with basis set and find that an extremely extended basis (triple zeta sp, diffuse sp, triple zeta d, double zeta f ) for GVB yields ΔEST=9.03 kcal/mol, in excellent agreement with the experimental value of 9.09±0.20 kcal/mol.
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  • 7
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We extend our recently reported embedding theory [J. Chem. Phys. 110, 7677 (1999)] to calculate not only improved descriptions of ground states, but now also localized excited states in a periodically infinite condensed phase. A local region of the solid is represented by a small cluster for which high quality quantum chemical calculations are performed. The interaction of the cluster with the extended condensed phase is taken into account by an effective embedding potential. This potential is calculated by periodic density functional theory (DFT) and is used as a one-electron operator in subsequent cluster calculations. Among a variety of benchmark calculations, we investigate a CO molecule adsorbed on a Pd(111) surface. By performing complete active space self-consistent field, configuration interaction (CI), and Møller–Plesset perturbation theory of order n (MP-n), we not only were able to obtain accurate adsorption energies via local corrections to DFT, but also vertical excitation energies for an internal (5σ→2π*) excitation within the adsorbed CO molecule. We demonstrate that our new scheme is an efficient and accurate approach for the calculation of local excited states in bulk metals and on metal surfaces. Additionally, a systematic means of improving locally on ground state properties is provided. © 2002 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7081-7085 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a pseudospectral formulation of the single reference, closed shell double excitation configuration interaction method using a generator state self-consistent electron pair approach. The method scales as O(n2N3), compared to the conventional scaling of O(n2N4+n3N3). In no case tested does the pseudospectral energy differ by more than 0.35 mhartree from the conventional result.
    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 105 (1996), S. 6455-6470 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new approximate correlation method has been developed by application of the local weak pairs approximation of Sæbø and Pulay to pseudospectral singles and doubles configuration interaction (SDCI) as developed by Martinez and Carter. The combination of the localization and pseudospectral approximations attacks both the problems of two-electron integral storage on disk and CI vector storage in memory that, respectively, hinder nondirect local spectral and nonlocal pseudospectral SDCI calculations individually and provides a scaling advantage over even direct local spectral SDCI calculations. The reproduction of total energies to within a kcal/mol leads to speed increases with respect to nonlocal calculations that grow larger with increasing molecular size: little or no savings for ethane and a factor of 1.1–1.6 for larger molecules studied (glyoxal, glycine, C6H2, and C8H2). The prediction of conformational energy differences with the new method appears quite promising, since energy difference predictions accurate to within a kcal/mol of the exact energy differences are obtained even when the single-point total energies are individually many kcal/mol in error. The speed increases for energy difference predictions of both local spectral and pseudospectral SDCI also grow with molecular size: from a factor of 4 in ethane and glyoxal to a factor of 6 in glycine. Additionally, when compared to the exact spectral result, the fastest local pseudospectral prediction of the conformational energy difference in glyoxal is in error by 0.2 kcal/mol and saves a factor of 10 in CPU time, indicating the prospects of combining local correlation and pseudospectral methods. © 1996 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 1251-1256 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an algorithm that is a new combination of the direct inversion in the iterative subspace (DIIS) and the generalized valence bond (GVB) methods. The proposed algorithm is based on applying the DIIS directly to the orbitals updated via the GVB scheme as opposed to the conventional approach of applying DIIS to a series of composite Fock matrices (CFMs). The new method results in GVB convergence in situations where the CFM-based GVB-DIIS cannot be applied at all, e.g., when the original GVB method diverges. When both the new and the conventional methods converge, the former achieves the same reduction in the number of self-consistent field (SCF) iterations as the latter, but using considerably less storage and DIIS-related CPU time. Also, the orbital-based GVB-DIIS is less sensitive to the proximity of an initial guess to the exact wave function, and it does not depend on empirical criteria used in the CFM-based GVB-DIIS. Finally, the orbital-based DIIS formulation is not limited to GVB; it can be easily incorporated into any SCF approach that involves an iterative updating of the orbitals, such as, e.g., multiconfiguration SCF or Kohn–Sham density-functional theory. © 1995 American Institute of Physics.
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