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  • 1
    Electronic Resource
    Electronic Resource
    Multireference and relativistic effects in NiH (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3589-3595 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Large multireference CI calculations have been performed for the ground state of NiH. The effects of relativity were investigated using both a variational (no pair) theory and perturbation theory. The largest CI calculations included up to 29 reference states and were performed at the contracted CI level. The calculated and experimental results (within parentheses) are for Re 2.76 a0 (2.76 a0), for ωe 1997 cm−1 (2003 cm−1) and for the dipole moment μ 2.32 D (2.4±0.1 D). The effects of relativity are −0.03 a0, +60 cm−1 and −0.3 D, respectively. The effects of going from a reference selection threshold of 0.05 to a selection threshold of 0.02 and a different set of CASSCF orbitals was before applying Davidson's correction +0.07 a0 for Re and about +30 cm−1 for ωe, and after applying this correction +0.06 a0 and −80 cm−1, respectively. The most accurate results for the dipole moment was obtained using the multireference ACPF method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456891
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  • 2
    Electronic Resource
    Electronic Resource
    A theoretical description of the b 3Π→a 3Σ+ transition of NO+ (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 5617-5625 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using multireference configuration interaction methods, the potential energy curves of the ground and several low-lying excited states of the NO+ ion were calculated. We obtain spectroscopic parameters in good agreement with existing experimental data. In order to establish a one-to-one correspondence between the experimentally known term energies of the recently detected b 3Π→a 3Σ+ transition [Huber and Vervloet, J. Mol. Spectrosc. 146, 188 (1991)] and ab initio data, it is necessary to include explicitly spin–orbit and rotational coupling. Spin–orbit matrix elements were evaluated using the microscopic Breit–Pauli Hamiltonian. The off-diagonal coupling matrix elements 〈b 3Π||HSO||a 3Σ+〉 and 〈b 3Π||L||a 3Σ+〉 are found to depend strongly on the internuclear separation. The calculated vibrationally averaged fine structure parameter of the b 3Π state for v=0 (67.21 cm−1) is found to be in very good agreement with the value determined experimentally (69.699 cm−1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467240
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio study of the vibronic and spin–orbit coupling in the X 2Πu state of C2H+2 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7142-7149 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A variational approach for treating the Renner–Teller effect in tetra-atomic molecules [Peric et al., Mol. Phys. 55, 1159 (1985)] is extended to account for the effect of spin–orbit coupling. The approach is applied to compute the spin–orbit splittings of the vibronic levels in the X 2Πu state of C2H+2. The bending potential curves employed in a previous study [Peric and Peyerimhoff, J. Chem. Phys. (in press)] are improved by carrying out ab initio calculations at a higher level of sophistication. The results of the computations enable a reliable interpretation of recent experimental findings [Pratt et al., J. Chem. Phys., 99, 66 (1993)]. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469108
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  • 4
    Electronic Resource
    Electronic Resource
    Spin-free relativistic no-pair ab initio core model potentials and valence basis sets for the transition metal elements Sc to Hg. Part I (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3678-3686 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Relativistic one-component ab initio core model potentials are presented for first-, second-, and third-row transition elements; corresponding valence spaces comprise the ns, (n−1)d, and (n−1)p shells. Direct relativistic effects on the valence electrons are explicitly taken into account by using one-component relativistic kinetic energy and Douglas–Kroll transformed no-pair nuclear attraction interaction operators. The Coulombic part of the atomic core–valence interaction has been fitted to the corresponding all-electron mean-field operators whereas a matrix representation has been chosen for the exchange part. While not involved in the fitting process, all-electron orbital energies and radial expectation values of the valence orbitals are very well reproduced in atomic model potential calculations. Molecular test calculations have been performed on selected transition metal oxides. Employing a [4s,4p,4d] contraction of the valence basis, excellent agreement between core model potential and all-electron no-pair results is achieved for bond distances, harmonic frequencies, and dissociation energies. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478257
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  • 5
    Electronic Resource
    Electronic Resource
    Relativistic ab-initio calculations on PdH and PdD: The rovibronic spectra and rotational splittings (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3517-3521 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An ab initio theoretical analysis of the rovibronic spectra of the PdH molecule and its heavier isotope PdD is presented. Potential curves of the lowest ΛS state multiplet 2Σ+, 2Δ, and 2Π are generated in consideration of kinematic relativistic effects in a one-component formalism. We determine the effects of the rotational motion of the nuclei on the vibronic spectra by evaluating matrix elements of a rotational Hamiltonian in the basis of uncoupled vibronic Born–Oppenheimer functions, including the effects of spin-orbit coupling and compare our results to experiment. Moreover, we present predictions for experimentally yet unknown transitions by calculating energy levels, Ω-, and vibrational splittings of several excited states. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475346
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  • 6
    Electronic Resource
    Electronic Resource
    Ab initio determination of electronic energy splitting and transition rates for imidogen in argon matrixes (1993)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 10011-10020 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100141a020
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical study of the electronic spectrum of the CoH molecule (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 1215-1223 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Calculated potential energy curves and spectroscopic parameters of the ground and various low-lying excited states of the cobalt hydride molecule are presented. Over 30 electronic states of singlet, triplet, and quintet multiplicity have been obtained with adiabatic excitation energies below 4 eV. In addition, the electronic structure of several negative ion states has been determined. CoH− possesses a 4Φ electronic ground state and at least three other electronic states that are stable with respect to electron autodetachment. The calculations include relativistic effects variationally by employing a one-component no-pair operator with external-field projectors. Electron correlation is accounted for by using multireference single and double excitation configuration interaction methods. Several experimentally observed bands in the optical spectrum of CoH are ascribed to transitions between the X 3Φ ground state and excited states of 3Φ, 3Δ, and 1Γ symmetry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465365
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  • 8
    Electronic Resource
    Electronic Resource
    The performance of energy extrapolation procedures in truncated averaged coupled-pair functionals (1994)
    Springer
    Theoretical chemistry accounts 88 (1994), S. 13-27 
    Details
    ISSN: 1432-2234
    Keywords: Averaged coupled-pair functionals ; Energy extrapolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Energy extrapolation techniques in conjunction with individual configuration selection are applied to averaged coupled-pair functional expansions. In order to test the quality of this approach, benchmark calculations have been performed for N2, the open and ring forms of O3, and for the ground and several excited states of CuH and PdH. Reliable energy estimates are obtained for N2 and the two transition metal hydrides and spectroscopic properties are in close agreement with the values for the non-truncated expansions. In the case of O3 the perturbation corrections substantially underestimate the complete singles and doubles results. These deviations cancel to a large extent, however, in the calculated isomerization energy. The accuracy of the one-particle density matrix is examined by computing dipole moments for several electronic states of CuH and PdH. Deviations are significant in some cases. For the evaluation of properties the current approach requires modifications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113730
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  • 9
    Electronic Resource
    Electronic Resource
    Spinor optimization for a relativistic spin-dependent CASSCF program (1997)
    Springer
    Theoretical chemistry accounts 97 (1997), S. 125-135 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Relativistic two-component quantum chemical methods ; Complete-active-space-SCF theory ; Spin-orbit coupling ; Spin-dependent one-particle bases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. Detailed formulae for the implementation of the multi-configuration SCF spinor optimization in a basis of Kramers pair 2-spinors – i.e. exploiting time-reversal symmetry – are presented. Full expressions for the spinor gradient and spinor Hessian elements are given in abstract form as well as within the usual CASSCF subspace division. As far as possible, the resulting terms are grouped to relativistic inactive and active Fock matrices, which have been introduced previously. Approximations for the Hessian are introduced so as to initialize it in an inverse Hessian update algorithm for a diagonal first approximation within the standard quasi-Newton-Raphson procedure. The effects of double group symmetry arising from spin dependence on Fock matrices and therefore gradient and Hessian are discussed and a group scheme for the implementation is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050245
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  • 10
    Electronic Resource
    Electronic Resource
    Ab initio prediction of 15N-NMR chemical shift in α-boron nitride based on an analysis of connectivities (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 716-725 
    Details
    ISSN: 0192-8651
    Keywords: NMR ; boron nitride ; solid state ; theoretical chemistry ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Hydrogen-saturated cut-outs of hexagonal boron nitride have been used to model the solid state. Model compounds have been geometry optimized by means of density functional theory, whereas chemical shift calculations have been carried out at the coupled-perturbed Hartree-Fock level of theory employing gauge-including atomic orbital (GIAO) basis sets. The reliability of results has been tested against experimental values for chemical shifts in stable molecules with similar structural elements. With increasing cluster size, viz. a vanishing influence of the saturating hydrogens on the innermost nitrogen atoms, we find a convergence of 15N chemical shifts. A classification scheme for the chemical environment of a nitrogen atom has been set up according to its bonding graph including the second coordination sphere. For a given connectivity, chemical shifts vary within a few parts per million, thus enabling us to predict a 15N-NMR chemical shift of -285 ± 5 ppm for solid α-boron nitride.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 716-725, 1998
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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