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  • 1
    Electronic Resource
    Electronic Resource
    Infinite-order two-component theory for relativistic quantum chemistry (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 2696-2704 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method for the iterative algebraic generation of the numerically accurate two-component Hamiltonian for the use in relativistic quantum chemistry is presented. The separation of the electronic and positronic states of the Dirac Hamiltonian is accomplished by the algebraic solution for the Foldy–Wouthuysen transformation. This leads to the two-component formalism whose accuracy is primarily limited by the choice of basis functions. Its performance is tested in calculations of the most sensitive 1s1/2 energy for increasing values of the nuclear charge. These calculations show that the electronic part of the Dirac eigenspectrum can be obtained from the two-component theory to arbitrarily high accuracy. Moreover, if needed, the positronic states can be separately determined in a similar way. Thus the present method can be also used for the evaluation of quantum electrodynamic corrections in the finite basis set approximation. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1436462
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  • 2
    Electronic Resource
    Electronic Resource
    Electric properties of diatomic interhalogens. A study of the electron correlation and relativistic contributions (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2048-2053 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently developed polarized basis sets for halogen atoms are used to calculate several basic electric properties of diatomic interhalogen molecules. In the valence approximation the electron correlation contribution is treated at the level of the fourth-order many-body perturbation theory approximation. The corresponding results are corrected for the core-polarization and relativistic effects. It is shown that the dipole moments of heavy interhalogen diatomics are considerably affected by the relativistic contribution, while the core-polarization effects are of lesser importance. The calculated, relativistically corrected, dipole moments are in agreement with experimental data and are used to discuss the reliability of the effective core potential approximation. The calculated quadrupole moments and parallel components of the dipole polarizability tensor are only marginally affected by contributions due to core-polarization and relativistic terms. The geometry derivatives of dipole moments and dipole polarizabilities computed in this study can be used for the evaluation of intensities in infrared and Raman spectra of interhalogen diatomics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462056
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  • 3
    Electronic Resource
    Electronic Resource
    Estimates of relativistic contributions to molecular properties (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8122-8132 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A simple method for the estimation of the relativistic contribution to atomic and molecular properties is proposed. The method assumes that the dominant portion of relativistic contribution to different properties is accounted for by the Cowan–Griffin operator. In contrast to recently investigated variational relativistic and quasirelativistic approaches, the present method is based virtually on the triple-perturbation theory approach and can be easily executed in the framework of the finite-field perturbation schemes. The method proposed in this paper is applied to the evaluation of the relativistic contribution to electric properties of hydrogen halides. This contribution turns out to be completely negligible in the case of HCl. For the HI molecule, the relativistic correction to its dipole moment becomes almost as important as the electron correlation effects. A similar result is also obtained in the case of the dipole moment of AgH. Different possible applications of the present method are discussed. The major advantage of the proposed perturbation approach is a very simple computational structure which permits the calculation of relativistic corrections from any available nonrelativistic wave function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459342
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  • 4
    Electronic Resource
    Electronic Resource
    A study of the accuracy of the CCSD+T(CCSD) approximation. Electric properties of KH and RbH (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 5490-5491 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461829
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  • 5
    Electronic Resource
    Electronic Resource
    The dipole moment of AuH (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2614-2622 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A finite-field perturbation approach is used to study the relativistic and relativistic-correlation contributions to electric properties of AuH. The relativistic terms in the molecular Hamiltonian are approximated by the so-called Cowan–Griffin perturbation operator whose first-order contributions are evaluated in a large basis set of Gaussian functions. The electron correlation contribution is accounted for by using the many body perturbation theory methods. Both the relativistic and electron correlation effects as well as the mixed relativistic-correlation contributions are shown to be important in accurate predictions of the dipole moment of AuH. According to the present study the dipole moment of the 1Σ+ ground electronic state of AuH calculated at the experimental equilibrium bond distance of 2.880 bohr is found to be in the range between 0.6–0.7 a.u. The quadrupole moment of AuH is shown to have positive sign in the relativistic-correlated treatment while its negative value is predicted in nonrelativistic calculations. The parallel component of the dipole polarizability tensor is found to be equal to about 44. a.u. It is also shown that the electric property values of AuH are strongly affected by the electron correlation effects involving the next-to-valence shell of the Au atom. The valence approximation gives quite unrealistic results for both the electron correlation and relativistic contributions to electric properties of AuH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460914
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  • 6
    Electronic Resource
    Electronic Resource
    Quadrupole moments of CuH, AgH, and AuH. A study of the electron correlation and relativistic effects (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8248-8253 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-level correlated calculations of the quadrupole moment of the group-Ib hydrides have been carried out with large Gaussian-type-orbital/contracted-Gaussian-type-orbital basis sets. The nonrelativistic results obtained for CuH, AgH, and AuH at the self-consistent-field Hartree–Fock level of approximation and for the origin at the heavy atom are −2.16, −3.17, and −1.94 a.u., respectively. The electron correlation contribution computed by using the coupled-cluster approaches reduces those values to −0.25, −1.14, and −0.18 a.u., respectively. The relativistic corrections have been obtained from the recently developed quasirelativistic method. They have been found to be of increasing importance for the investigated series of hydrides. The final relativistically corrected values of molecular quadrupole moments are found to be small for CuH (+0.05 a.u.) and AgH (−0.36 a.u.) while the corresponding value for AuH is large and positive (+2.00 a.u.).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461303
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  • 7
    Electronic Resource
    Electronic Resource
    Exact perturbation treatment of the basis set superposition correction (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 6705-6711 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is shown that a complete removal of the basis set superposition effect on the interaction properties of a composite system can be understood in terms of constraints imposed on its wave function. This interpretation of the basis set superposition effect is used to build variation methods which account for the constraints imposed by the incompleteness of available solutions for the constituent subsystems. A perturbation analysis of the resulting constrained equations provides an exact method for the evaluation of the basis set superposition contribution to interaction properties. The corresponding perturbation correction is explicitly evaluated for the Hartree–Fock approximation and discussed at the level of different correlated methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461540
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  • 8
    Electronic Resource
    Electronic Resource
    Quasirelativistic studies of molecular electric properties: Dipole moments of the group IVa oxides and sulfides (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 1345-1351 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dipole moments of SiO, GeO, SnO, PbO, and of the corresponding sulfides are computed by using a variety of high-level correlated methods and polarized basis sets of Gaussian functions. The contribution of relativistic effects has been accounted for by the first-order quasirelativistic approach based on mass-velocity and Darwin terms. The results for sulfides are in good agreement with experiment while for oxides seem to show a progressive deterioration with the increase of the heavy atom nuclear charge. The discrepancies between the calculated and experimental dipole moments for oxides have been carefully analyzed for the PbO molecule in terms of the basis set choice and reliability of the calculated electron correlation and relativistic corrections. The pattern of relativistic corrections computed in the present study is compared with that which follows from recent quasirelativistic and fully relativistic calculations of Dyall. Some complementary calculations of the dipole moment of PbSe and PbTe seem to indicate that both the polarized basis sets and computational methods used in this study should not fail to predict correct values of the dipole moment of PbO and other oxides of the group IVa atoms. The rather unexpected discrepancies have no plausible explanation within the range of methods employed in our study and offer a challenge for more advanced, fully relativistic molecular calculations at the correlated level of approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464301
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  • 9
    Electronic Resource
    Electronic Resource
    Second-order perturbation theory with a CASSCF reference function (1990)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 94 (1990), S. 5483-5488 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100377a012
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  • 10
    Electronic Resource
    Electronic Resource
    Reply to the Comment on: Exact perturbation treatment of the basis set superposition correction (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5259-5259 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463808
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