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  • 1
    Digitale Medien
    Digitale Medien
    Relativistic and correlated calculations on the ground, excited, and ionized states of iodine (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 9046-9058 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The electronic structure, spectroscopic, and bonding properties of the ground, excited, and ionized states of iodine are studied within a four-component relativistic framework using the MOLFDIR program package. The experimentally determined properties of the 1Σg+ ground state are well reproduced by our results calculated at the CCSD(T) level of theory. Relativistic effects and core–valence correlation need to be included in order to get reliable results, but the Gaunt interaction can be neglected. The photoelectron spectrum and the potential energy curves of the ionized and excited states are calculated using relativistic configuration interaction and coupled cluster methods. The calculated properties of the excited states are generally in good agreement with the experimental data, as well as with the earlier theoretical results of Teichteil and Pelissier. An alternative assignment of some recently measured, low lying, ionized states is proposed. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.475194
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  • 2
    Digitale Medien
    Digitale Medien
    On the magnetic coupling in NiO (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3287-3291 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The results are reported of ab initio calculations on the magnetic ordering in NiO, a prototype of the antiferromagnetic insulator. By analyzing wave functions for different cluster models, information is obtained about the physical effects determining the sign and the magnitude of the magnetic coupling parameter J. The role of the edge oxygens, surrounding the essential unit (Ni2O), is found to be quantitatively important but purely environmental in contrast to the role of the bridging oxygen. Furthermore, the importance of electron correlation and the usefulness of pseudopotentials in the calculations is investigated. The final result for J compares reasonably with experiment (about 50%), and possible sources for the remaining discrepancies are discussed. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.473065
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  • 3
    Digitale Medien
    Digitale Medien
    Theoretical characterization of the low-lying excited states of the CuCl molecule (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 7162-7169 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The character of the low-lying excited states of diatomic CuCl is studied primarily by means of the complete active space self-consistent field (CASSCF), method and a second order perturbation approach with the CASSCF wave function as reference state [complete active space perturbation theory to second order (CASPT2)]. For comparison, the lower levels of the spectra of the Cu+ ion are also analyzed. A first order treatment of the scalar relativistic effects, the mass–velocity and Darwin terms, is included in the calculations. The importance of spin–orbit interactions is investigated by comparing our nonrelativistic valence shell CI (VCI) and relativistic results obtained with our four-component program suite MOLFDIR. The six lowest excited states of the CuCl molecule, which are related to the Cu+(3d94s1)Cl−(3s23p6) ionic configuration, are assigned. The assignments agree with earlier theoretical work. Where they can be compared, the calculated spectroscopic constants are in good agreement with the experimental data. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.473161
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  • 4
    Digitale Medien
    Digitale Medien
    The electronic structure of the PtH molecule: Fully relativistic configuration interaction calculations of the ground and excited states (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6704-6715 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Fully relativistic all-electron self-consistent field calculations based on the Dirac–Coulomb Hamiltonian have been performed on the three lowest lying states of the PtH molecule. The resulting four-component Dirac–Hartree–Fock (DHF) molecular spinors are subsequently used in relativistic configuration interaction (CI) calculations on the five lower states of PtH. Spectroscopic properties are obtained by fitting the potential curve to a Morse function and show good agreement with experimental data. The effect of relativistic corrections to the Coulomb electron–electron interaction is investigated at the DHF level and is found to be insignificant for the molecular spectroscopic properties investigated by us. The CI wave functions are found to have only one dominant configuration, indicating a lack of static correlation. Dynamic correlation in the d shell is, however, important for the spectroscopic properties of PtH. The results conform with a bonding scheme in which the three lower and two upper states of PtH are assigned 5d3/245d5/25σ1/22 and 5d3/235d5/26σ1/22 electronic configurations, respectively. The configurations are only approximate and are perturbed by 5d participation in bonding. The stability of the Pt–H bond is explained in terms of the relativistic stabilization of the 6s orbital in analogy with the electron affinity of the platinum atom.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.465813
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  • 5
    Digitale Medien
    Digitale Medien
    Molecular open shell configuration interaction calculations using the Dirac–Coulomb Hamiltonian: The f 6-manifold of an embedded EuO9−6 cluster (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2910-2919 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We present results of all-electron molecular relativistic (Hartree–Fock–Dirac) and nonrelativistic (Hartree–Fock) calculations followed by a complete open shell configuration interaction (COSCI) calculation on an EuO9−6 cluster in a Ba2GdNbO6 crystal. The results include the calculated energies of a number of states derived from the f6−manifold and 5D–7F luminescence transition wavelengths. The calculations were performed using the molecular Fock–Dirac (molfdir) program package developed in our laboratory. The theory and methods employed in this package are briefly described. The physical models used to analyze the Eu3+ impurity states range from a bare Eu3+ ion to an EuO9−6 cluster embedded in a Madelung potential representing the rest of the crystal. We show that it is necessary to use the embedded cluster model to get a reasonable description of the crystal field splittings of the states arising from the f6-manifold. Our results indicate that the calculated splittings are very sensitive to the orbitals used. It is therefore essential that relativistic orbitals be used from the outset.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461987
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  • 6
    Digitale Medien
    Digitale Medien
    Relativistic and correlation effects on molecular properties. II. The hydrogen halides HF, HCl, HBr, HI, and HAt (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1987-1994 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A benchmark study of a number of four-component relativistic correlation methods is presented. Bond lengths, harmonic frequencies, and dissociation energies of the molecules HF, HCl, HBr, HI, and HAt are calculated at various levels of theory, using both the Schrödinger and the Dirac–Coulomb–(Gaunt) Hamiltonian. The inclusion of relativity leads to a weakening of the bond, giving a decrease in the calculated harmonic frequencies and dissociation energies of the hydrogen halides. The effect on the bond length is small. These trends are explained by considering the relativistic change in hybridization induced by the spin–orbit coupling. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.472066
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  • 7
    Digitale Medien
    Digitale Medien
    Chemical lasers II (1965)
    Springer
    Zeitschrift für angewandte Mathematik und Physik 16 (1965), S. 107-110 
    Details
    ISSN: 1420-9039
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Physik
    Notizen: Abstract A short survey is given of population inversions resulting from chemical reactions. The way in which the possibilities for realisation of a chemical laser are investigated by us is discussed and the results obtained are given.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01589067
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  • 8
    Digitale Medien
    Digitale Medien
    Chemical lasers I (1965)
    Springer
    Zeitschrift für angewandte Mathematik und Physik 16 (1965), S. 101-106 
    Details
    ISSN: 1420-9039
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Physik
    Notizen: Abstract The concept of a chemical laser is discussed and a preferable definition is proposed. In order to obtain some insight into the feasibility of chemical pumping in general and into the orders of magnitude of the parameters involved, the consequences of a simple model, more or less related to a stationary “flamelaser”, are explored. According to this model i) a lower limit depending on flow velocity and wavelength exists for the rate at which production and radiative processes may proceed, and ii) the available gain can very appreciably exceed the critical value needed for laser action if certain conditions are satisfied. The assumptions underlying the model and its results, and their applicability in practice are briefly discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01589066
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  • 9
    Digitale Medien
    Digitale Medien
    Broken orbital symmetry and the description of valence hole states in the tetrahedral [CrO4]2− anion (1988)
    Springer
    Theoretical chemistry accounts 73 (1988), S. 405-418 
    Details
    ISSN: 1432-2234
    Schlagwort(e): Valence hole states ; Symmetry breaking ; Localized orbitals
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The localization of ligand-based valence holes in the tetrahedral complex ion [CrO4]2− in a crystalline environment is studied by SCF calculations on the hole states, with progressively less restrictions on the spatial symmetry of the molecular orbitals. The final wavefunctions are obtained by constructing, from the symmetry broken SCF solutions, wavefunctions that exhibit again the proper transformation properties under the operations of T d . The crystal environment of the [CrO4]2− anion is represented by a point charge model. In contrast with the situation for core hole states, the projection afterwards into T d symmetry is important. The final ionization energies, which are obtained from projected C 3v adapted SCF solutions, are reduced considerably (≅3 eV) with respect to the T d ΔSCF results, but the ordering of the states has not changed essentially. The calculated ionization energies compare favourably with results of XPS experiments on Na2CrO4. The evaluation of the energies of projected symmetry broken SCF solutions requires the calculation of hamiltonian matrix elements between determinantal wavefunctions built from mutually non-orthogonal orbital sets. An efficient method for the calculation of such matrix elements is presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00527744
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  • 10
    Digitale Medien
    Digitale Medien
    Relativistic all-electron molecular Hartree-Fock-Dirac-(Breit) calculations on CH4, SiH4, GeH4, SnH4, PbH4 (1992)
    Springer
    Theoretical chemistry accounts 81 (1992), S. 405-416 
    Details
    ISSN: 1432-2234
    Schlagwort(e): Relativisticab initio calculations ; Hartree-Fock-Dirac method ; Breit interaction ; Tetrahedral hydrides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Results and details of molecular Fock-Dirac-(Breit) calculations on CH4, SiH4, GeH4, SnH4, and PbH4 obtained with the MOLFDIR© program package are presented and compared with other calculations and experimental results. The relativistic ground state energies (including the Breit interaction) of the atoms C, Si, Ge, Sn, and Pb, necessary for reference purposes, have been calculated using a small relativistic CI. One of our findings is that for the heavier systems perturbation theory over-estimates the relativistic bond length contraction. The Breit interaction has only a small effect on the bond lengths.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01134864
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