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  • 1990-1994  (28)
  • 1985-1989  (20)
  • 1
    Electronic Resource
    Electronic Resource
    Ionic states of nitrosyl cyanide (1985)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 89 (1985), S. 1384-1387 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100254a015
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Quasidiabatic states from ab initio calculations by block diagonalization of the electronic Hamiltonian: Use of frozen orbitals (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 6668-6680 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The construction of quasidiabatic states is of theoretical and practical relevance in treating systems that exhibit strong nonadiabatic interactions. In the present work the implementation of the recently proposed method of block diagonalization of the electronic Hamiltonian in CI-type calculations, both theoretically and in practical calculations is investigated in detail. It is shown that the use of shifted or frozen molecular orbitals in the calculation of the adiabatic potential energy surfaces provides the most appropriate N-electron wave functions for applying the block diagonalization procedure. Freezing means to conserve the composition of the molecular orbitals at some chosen geometry, i.e., to have their coefficients unchanged with respect to the atomic orbitals with varying nuclear geometry. The use of the frozen orbitals and block diagonalization of the resulting CI matrix yields a method that treats orbital coupling and configurational interaction efficiently at the same time, leading to quasidiabatic states. Due to the mathematical simplicity of the method and to the fact, that no derivative couplings are needed during the calculations, the additional computational cost is negligible. Application to the ethylene dication illustrates the successful performance of the proposed method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461537
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Erratum: Gauge theory and quasidiabatic states in molecular physics [J. Chem. Phys. 91, 7057 (1989)] (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5166-5166 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458621
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Valence ionization of HCl. An investigation of many-body effects (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4331-4341 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Many-body Green's-function calculations which employ large configurational expansions and which are accurate to third and fourth order of perturbation theory are reported for the valence ionic states of HCl. Large polarized basis sets including Rydberg functions s-, p-, and d-type symmetries have been used. Third-order calculations are sufficient in the outer valence region, but in the inner valence region where the complete breakdown of the one-particle picture of ionization is observed a fourth-order theory is necessary in conjunction with large basis sets. The synchrotron and x-ray excited spectra can be assigned nearly up to the double-ionization threshold in a very satisfactory way. No indication of strong outer valence satellite lines is found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457740
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Doubly ionized states of ethylene: Auger spectrum, potential energy surfaces and nuclear dynamics (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1734-1753 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Theoretical investigations of the outer valence doubly ionized states of ethylene are presented using ab initio Green's function and configuration interaction methods. The vertical double ionization potentials computed by the Green's function method using the ADC(2) scheme are discussed in connection with the Auger spectrum of ethylene and found to reproduce the experimental spectrum quite accurately. Another main purpose of the present work is the investigation of the potential energy surfaces of selected states via ADC(2) and the study of the nuclear dynamics on them. It is shown that only the ground state of the dication is nonplanar with a torsional angle of 90°. The investigation of the topology of the surfaces reveals a low energy conical intersection of the dicationic ground and first excited states. The associated vibronic coupling problem turns out to include, additionally, the second excited state and thus, we encounter here a three-state problem. In the approximation of linear vibrational and vibronic coupling the static and dynamic aspects of the vibronic interaction are investigated by a model Hamiltonian comprising three nonseparable nondegenerate vibrational modes. The input data for the model are extracted from the ADC(2) results. With the aid of this Hamiltonian we have computed a hypothetical "sudden'' double ionization spectrum of ethylene whose complex structure is analyzed stepwise and by cuts through the pertinent adiabatic and diabatic surfaces. The analysis exhibits that the conical intersection of the two lower lying states dominates the vibronic dynamics and leads to strong vibronic mixing between them. This mixing is indirectly reinforced by the interaction between the intermediate and the upper states. As a consequence, strong nonadiabatic effects occur in the ethylene dication. Furthermore, two of the three surfaces involved in the conical intersection are also involved in a multidimensional avoided crossing. A more detailed analysis presented earlier has exhibited that the states belong to an interesting class where two potential energy surfaces are likely not to coincide although plenty of nuclear degrees of freedom exist, in principle, to allow for an intersection to occur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457080
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Valence ionization and the electron affinities of the open and cyclic forms of Se3 and Te3 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3582-3588 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Se3 and Te3 exist as the S3 molecule in an open C2v and a closed D3h form with different electronic configurations but nearly the same total energy. The ionization spectra of Se3 and Te3 are calculated in both the C2v and D3h forms by many-body Green's function methods. The D3h forms behave quite regularly, but very strong correlation effects are found in the C2v forms. If a theory accurate to third order is used, satellite lines appear at the ionization threshold. If higher order terms are included the satellite lines at the ionization threshold experience a slight change in energy, but a considerable reduction of intensity. Se3 has a positive electron affinity in both the C2v and D3h forms (2B1, 2A'2, states), and Te3 appears to have two positive electron affinities (2B1, 2A1 for the C2v form and 2A2 and 2E' for the D3h form).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456890
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Symmetry breaking and symmetry restoring in ions of loosely bound systems (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7039-7047 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a theoretical analysis of the effects that lead to distortion or symmetry restoration of the nuclear configuration in ions of weakly bound molecular systems and clusters. The vibronic coupling mechanisms involved are reviewed and discussed in terms of simple and general models. Guided by a qualitative characterization of the wave function of a loosely bound system, we study the symmetry determining effects for such ions in terms of first order (Koopmans'), relaxation and correlation distortion energies associated with electron removal from the parent system. Our discussion suggests that the Koopmans' approximation can reasonably be expected to provide a qualitatively correct dependence of the ion energy on nuclear motion. Exceeding these expectations, it is found in numerical applications to the He+3 and He+4 ions that the relaxation and correlation energy changes accompanying symmetry breaking tend to cancel exactly. This implies, and we show in practice, that while insufficiently accurate correlation energy estimates may easily lead to incorrect geometries, the inexpensive Koopmans' approximation can often suffice to obtain the correct energy curvature along symmetry breaking coordinates. Further preliminary results for N3 and CO+2 suggest that these findings have a much wider applicability than anticipated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457321
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Multiconfigurational time-dependent Hartree study of complex dynamics: Photodissociation of NO2 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 9062-9071 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The multiconfigurational time-dependent Hartree (MCTDH) approach is applied to an example showing very complex dynamics: the wave-packet dynamics on the three-dimensional B2 potential-energy surface of NO2. The ability of the MCTDH scheme to describe accurately the severe splitting of the wave packet on a saddle-shaped surface is demonstrated. Internal checks of the MCTDH calculation enable us to assess the degree of convergence without the need to resort to a numerically exact wave-packet calculation. As a representative observable the photodissociation spectrum is calculated and discussed. The A1/B2 vibronic coupling is neglected in our study, but the dynamics on the diabatic B2 surface is treated in its full three dimensionality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463332
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Statistical fluctuations of decay rates (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3934-3947 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We introduce a general Hamiltonian describing two coupled subsystems, each having a finite zero-order decay probability. With use of simple statistical assumptions on the underlying states, we derive new probability distributions of individual decay rates. We analyze the cases of weak and intermediate to strong coupling, respectively. The resulting distributions often resemble a suitable χ2 distribution, but do not belong to that class of functions. An interpretation of decay rates in terms of a χ2 model thus may lead to wrong conclusions. As a concrete realization, we study a Hamiltonian describing the non-Born–Oppenheimer coupling of two electronic states via the nuclear motion. The model is applied to the calculation of absorption-type spectra of NO2 and C2H+4. We investigate statistical properties of energy levels, line intensities, and decay rates. For NO2, we find from all statistics a completely irregular behavior, consistent with random matrix predictions and demonstrating the strong mixing of zero-order states due to the nonadiabatic coupling. For C2H+4, all statistics exhibit characteristic deviations from the irregular limit that can be given a consistent interpretation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456825
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Wave-packet dynamics within the multiconfiguration Hartree framework: General aspects and application to NOCl (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3199-3213 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The multiconfigurational time-dependent Hartree (MCTDH) approximation to the time-dependent Schrödinger equation is tested for a realistic three-dimensional example, the photodissociation of NOCl. The working equations of the MCTDH scheme introduced earlier are discussed in some detail. A computational scheme is presented which allows for efficient numerical MCTDH calculations. This scheme is applied to the photodissociation of NOCl after excitation to the S1 surface. The results are compared to the results of an exact wave-packet dynamics calculation. Fast convergence of the MCTDH results toward the exact one is found as the number of configurations is increased. The computation times of the MCTDH calculations are found to be much shorter than those of the exact calculation. Even MCTDH calculations including sufficiently many configurations for a fully converged (quasiexact) description require over two orders of magnitude less CPU time than an exact calculation. The so-called "natural populations'' that are computed along with the MCTDH wave packet serve as a check of the degree of convergence without the need to resort to an exact (or more accurate) calculation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463007
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    Paper (German National Licenses)
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