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  • Articles  (210)
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  • Articles  (210)
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  • 1
    Electronic Resource
    Electronic Resource
    Electronic structure of main-group-element-centered octahedral gold clusters (1991)
    s.l. : American Chemical Society
    Inorganic chemistry 30 (1991), S. 3986-3994 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00021a005
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  • 2
    Electronic Resource
    Electronic Resource
    A molecular orbital study of bonding and ionization energies in pentavalent uranium imide/amide complexes (1992)
    s.l. : American Chemical Society
    Inorganic chemistry 31 (1992), S. 577-581 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00030a010
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular photo cross sections with the LCGTO–Xα method using Stieltjes imaging (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5563-5572 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method for calculating and symmetry analyzing total molecular photoionization cross sections is presented. The technique is based on the LCGTO–Xα method and employs Stieltjes imaging. It allows applications to molecular systems comparable in size to those treated so far with the continuum multiple-scattering Xα method, but avoids the pitfalls of the muffin-tin approximation to the electronic potential. Photo cross sections for valence ionization of CO are found in good agreement with experiment and with previous calculations. From a final state symmetry analysis for the 1π level, the absence of kσ* shape resonance which appears in the 4σ and the 5σ ionization channels is attributed to small transition moments. This is in contrast to a previous treatment where this difference has been rationalized as caused by a channel dependent final state potential. The photoionization cross sections for the four highest valence orbitals of benzene were calculated in better agreement with experiment than found in a previous Xα–SW treatment. The improvement is especially significant for the 1e1g(π) highest occupied molecular orbital where at least part of the experimentally observed structures are attributed to shape resonances. Some of the observed resonance features in the valence orbital photo cross sections of benzene were identified with resonances found in carbon K-shell ionization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459626
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  • 4
    Electronic Resource
    Electronic Resource
    An efficient method for calculating molecular excitation energies by time-dependent density-functional theory (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 2088-2099 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new efficient method for determining excitation energies and oscillator strengths of molecules which is based on time-dependent density functional theory (TDDFT). It yields the valence excitation spectrum of a molecule at a fraction of the computational effort necessary for the corresponding ground state calculation. The efficiency of the method originates in the extensive use of auxiliary basis sets. Nevertheless this approach does not lead to significant inaccuracies. The method is applied to benzene, naphtalene, and the higher linearly annelated polycyclic aromatic hydrocarbons anthracene to heptacene. Features and trends in the excitation spectra of these aromatic hydrocarbons are well described by the new TDDFT method. The standard basis sets commonly used in TDDFT based procedures are found to be inadequate for an accurate treatment of excitations into Rydberg-type states. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.482020
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  • 5
    Electronic Resource
    Electronic Resource
    The asymptotic region of the Kohn–Sham exchange potential in molecules (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 5374-5388 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Kohn–Sham exchange potential is shown to approach on nodal surfaces of the energetically highest occupied orbital different asymptotic limits than in other regions. This leads to strong anisotropies and barrier–well structures in the near-asymptotic region. Effective exact-exchange potentials, like the one obtained in the recently introduced localized Hartree–Fock method, exhibit the correct asymptotic limits and the accompanying structures in the near-asymptotic region. An efficient, accurate method for the calculation of the Slater potential and of effective exact-exchange potentials in the asymptotic region is presented. The method is based on an asymptotic continuation of Kohn–Sham (KS) orbitals and is numerically stable up to arbitrary large distances from the molecule. It can easily be implemented in existing quantum chemistry codes employing Gaussian basis sets. The asymptotic region of effective exact-exchange potentials is shown to be different from the various asymptotically corrected exchange-correlation functionals and to strongly affect unoccupied KS orbitals. Results for small- and medium-size molecules are presented. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1453958
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  • 6
    Electronic Resource
    Electronic Resource
    Efficient localized Hartree–Fock methods as effective exact-exchange Kohn–Sham methods for molecules (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 5718-5732 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The form of the Kohn–Sham (KS) exchange potential, which arises from the approximation that the Hartree–Fock (HF) and the exchange-only KS determinant are equal, is derived. Two related procedures to determine the KS exchange potential follow from this approximation: a self-consistent localized HF procedure and a transformation localized HF procedure yielding the local KS exchange potential from HF orbitals. Both procedures can be considered as almost exact exchange KS methods which require only occupied orbitals and are invariant with respect to unitary transformations of the orbitals, i.e., depend only on the first order density matrix. The resulting local KS exchange potentials are free of Coulomb self-interactions and exhibit the correct long-range 1/r-behavior. The Krieger, Li, and Iafrate (KLI) procedure to determine the KS exchange potential can be considered as an approximation to the introduced localized HF procedures. Highly efficient methods to carry out the presented localized HF as well as KLI procedures are introduced. An efficient basis set approach to calculate the Slater potential is presented. The methods can easily be implemented in present standard quantum chemistry codes. Applications to small and medium size molecules and clusters are presented. The Hartree–Fock and the exchange-only KS determinant are found to be surprisingly close. Qualitatively correct, Coulomb self-interaction free KS orbitals and eigenvalue spectra are obtained. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1398093
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular photoionization cross sections by the Lobatto technique. I. Valence photoionization (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 2808-2820 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method for the calculation of electronic continuum wave functions is presented which is based on the logarithmic derivative version of the Kohn (LDK) variational principle. The variational principle is cast into algebraic form by introducing a finite basis set that consists of spherical harmonic Gaussian-type functions (GTOs) and of Lobatto shape functions with the latter representing the translational part of the basis. A local effective potential which is obtained from density functional theory results in fairly accurate photoionization cross sections. Also studied are asymptotic corrections to the effective potential for the photoelectron which, in many cases, lead to improved results. The Lobatto procedure is applied to the diatomics N2 and CO and to benzene which may be regarded as a prototype for larger non spherical symmetric systems for which the method is targeted. For the two diatomics, results in excellent agreement with experiment have been found. For benzene the results are compared to those obtained by the Stieltjes–Tchebychev (ST) imaging technique and by the continuum multiple scattering (CMS) method which both have been applied to similar effective local potentials. Comparison with the ST imaging technique shows that the LDK Lobatto (LDKL) method provides qualitatively similar results, but the LDKL cross sections are of higher resolution and allow a more detailed analysis because of the explicit determination of the continuum wave function. For most of the valence orbitals of benzene the CMS method does not lead to satisfactory agreement with experiment due to the well-known deficiencies of this technique. The LDKL method implemented with a combined basis set does not suffer from the limitations of the ST and the CMS methods, but remains applicable to larger-size molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466475
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  • 8
    Electronic Resource
    Electronic Resource
    Density- and density-matrix-based coupled Kohn–Sham methods for dynamic polarizabilities and excitation energies of molecules (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2785-2799 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Basis set methods for calculating dynamic polarizabilities and excitation energies via coupled Kohn–Sham equations within time-dependent density functional theory are introduced. The methods can be employed after solving the ground state Kohn–Sham equations with a fitting function approach. Successful applications of the methods to test molecules are presented. Coupled Kohn–Sham methods based on the linear response of the Kohn–Sham density matrix are derived from the standard coupled Kohn–Sham equation based on the linear response of the electron density and the relations between the two types of coupled Kohn–Sham equations are investigated. The choice of norm functions associated with basis set representations of the coupled Kohn–Sham equations is discussed and shown to be a critical point of basis set approaches to time-dependent density functional theory. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477922
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  • 9
    Electronic Resource
    Electronic Resource
    Closed-form expression relating the second-order component of the density functional theory correlation energy to its functional derivative (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6280-6286 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For helping to improve approximations to the density-functional exchange-correlation energy, Exc[n], and its functional derivative, the difference between the second-order component of the correlation energy, Ec(2)[n], and the integral ∫dr vc(2)([n];r)n(r), involving its functional derivative, vc(2)([n];r), is given in terms of only the occupied Kohn–Sham orbitals and the exchange potential. The quantity 2Ec(2)[n] is especially significant because it is the initial slope in the adiabatic connection formula for Exc[n]. The analytic expression for 2Ec(2)[n]−∫dr vc(2)([n];r)n(r) is obtained for any spherically symmetric two-electron test density. Numerical examples are presented. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477269
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  • 10
    Electronic Resource
    Electronic Resource
    Hybrid schemes combining the Hartree–Fock method and density-functional theory: Underlying formalism and properties of correlation functionals (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 2675-2680 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Hybrid schemes that combine elements of the Hartree–Fock and the Kohn–Sham procedures are shown here to have a rigorous formal basis within exact density-functional theory. Properties of the exact correlation energy and its functional derivative, corresponding to each hybrid scheme, are introduced and the correlation energy is expressed by a coupling constant integral. The coupling constant expansions of hybrid correlation energies are considered. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473369
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