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  • 1
    Electronic Resource
    Electronic Resource
    Quadratic response theory of frequency-dependent first hyperpolarizability. Calculations in the dipole length and mixed-velocity formalisms (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7251-7258 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The quadratic response function (QRF) is evaluated within the random phase approximation (RPA), to compute frequency-dependent first hyperpolarizabilities β(ω,ω). The method treats electron correlation consistent through first order, so the computed values are equivalent to coupled-perturbed Hartree–Fock (CPHF) results. The QRF is obtained by solving systems of linear equations, thus circumventing the RPA eigenvalue problem. The QRF equation of motion is used to develop hyperpolarizability identities in the dipole length and mixed-velocity representations. The two forms of β are equivalent at the RPA level, and provide a useful measure of completeness of basis. The method is applied to the hyperpolarizability of HF and H2O. It is found that basis sets used in previous studies were not saturated for all β components, and that basis sets which satisfy length–velocity sum rules for linear response properties are not sufficient for agreement of quadratic response properties. The calculated dispersion ratios are in good agreement with experimental measurement, indicating that dispersion effects are properly described by frequency-dependent calculations in the RPA at field energies which are small compared to vertical excitation energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460209
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  • 2
    Electronic Resource
    Electronic Resource
    Spin–spin coupling constants of CO and N2 (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2138-2142 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used the second order polarization propagator method to calculate the indirect nuclear spin–spin coupling constants of 13C–17O and 14N–15N. We have calculated all coupling terms and the vibrationally averaged results are for CO: JFC =7.93 Hz, JSD =−3.99 Hz, JPSO =14.95 Hz, JDSO =0.10 Hz, Jtotal(CO) =18.99 Hz and for N2: JFC =0.82 Hz, JSD =−1.57 Hz, JPSO =3.32 Hz, JDSO =0.03 Hz, and Jtotal(N2) =2.60 Hz. Recent measurements of the two coupling constants gave 1J(13C,17O)=16.4±0.1 Hz and 1J(14N,15N)=1.8±0.6 Hz.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453722
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  • 3
    Electronic Resource
    Electronic Resource
    Nuclear magnetic shieldings and spin rotation constants of HF and N2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6036-6042 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The paramagnetic contribution to the nuclear magnetic shieldings and the spin rotation constants are calculated using polarization propagator theory. Results are reported both in the first order approximation [equivalent to the coupled Hartree–Fock (CHF) method] and in the second order polarization propagator approximation (SOPPA). It is demonstrated how the constant Cgauge which gives the gauge origin dependence of the total nuclear magnetic shielding in a finite basis set [σ(Rc+d)=σ(Rc)+d⋅Cgauge] can be calculated from the polarization propagator. The magnetic shieldings of H and F in HF are nearly the same in CHF and SOPPA and results from both levels of theory agree well with experiment. For N2, σ(SOPPA)=−72.2 ppm, also in good agreement with the most recent measurement. However, for N2 there is a large correlation effect since σ(CHF)=−106.5 ppm. The computed spin rotation constant for N2 is M(15N)=20 kHz, i.e., about 2 kHz lower than its measured value. This value of M(15N) corresponds to σ(N)=−72.2 ppm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458375
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  • 4
    Electronic Resource
    Electronic Resource
    Electronic spectra and response properties of BH and AlH (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2338-2343 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have calculated ground-state potential-energy curves, vertical electronic excitation energies, transition moments, radiative lifetimes, and indirect nulcear spin–spin coupling constants of BH and AlH. The coupling constants are predicted to be J(11B–H)=49.40 Hz and J(27Al–H)=10.01 Hz. Total energies are obtained using the coupled clusters singles and doubles method while excitation energies and response properties are calculated by means of the coupled cluster polarization propagator method. It is essential for the agreement with experiment that the coupled cluster rather than the second-order polarization propagator method is applied. The lowest excitation energies of each symmetry are nearly the same in a CISD (CI singles and doubles) calculation as in the polarization propagator calculation and both methods agree well with experiment. However, orbitals optimized for the individual states are needed in the CISD calculation, whereas ground-state self-consistent field (SCF) orbitals may be used for all states in the propagator calculation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455975
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  • 5
    Electronic Resource
    Electronic Resource
    Relativistic four-component calculations of indirect nuclear spin–spin couplings in MH4 (M=C, Si, Ge, Sn, Pb) and Pb(CH3)3H (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 3493-3498 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Relativistic four-component random phase approximation (RPA) calculations of indirect nuclear spin–spin coupling constants in MH4 (M=C, Si, Ge, Sn, Pb) and Pb(CH3)3H are presented. The need for tight s-functions also in relativistic four-component calculations is verified and explained, and the effect of omission of (SS–LL) and (SS–SS) two-electron integrals is investigated. Already in GeH4 we see a relativistic increase in the coupling constant by 12%, and for PbH4 the effect is a 156% increase for the one-bond coupling. Large relativistic effects are also computed for the two-bonds couplings. We find that the relativistic effects on the one-bond couplings are mainly due to scalar relativistic factors rather than spin–orbit corrections. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480504
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  • 6
    Electronic Resource
    Electronic Resource
    The structure and spectrum of SiC2 (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1702-1708 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Second order polarization propagator calculations indicate that the blue/green bands attributed to SiC2 in the atmospheres of certain carbon stars arise from a triangular (C2v) form of the molecule. It appears that this form is separated from a linear (C∞v) form by only a very small barrier, and that spectra from both forms might be observable. The potential for the movement of Si around the C2 fragment, the spectral lines, oscillator strengths, and lifetimes are discussed. We find, as observed previously, that only in a correlated calculation is the triangular geometry the preferred ground state conformation. Also the excitation properties change markedly with correlation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449357
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  • 7
    Electronic Resource
    Electronic Resource
    Correlated dipole oscillator sum rules (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8969-8975 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The second order polarization propagator approximation (SOPPA) has been applied to the calculation of the dynamic dipole polarizability, α(ω), of the molecules N2, C2H2, CO, and HCN. The dipole oscillator sum rules S(−4) and S(−6), which are the leading contributions to the Cauchy expansion of the polarizability, have also been evaluated at SOPPA level, using a polynomial fit to this expansion. These are the first reported values of the higher sum rules obtained using the SOPPA approach, and we observe excellent agreement with experiment. We also discuss the applicability of scaling or additivity expressions for obtaining the correlated polarizability from static correlated and dynamic uncorrelated quantities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466701
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  • 8
    Electronic Resource
    Electronic Resource
    A coupled cluster polarization propagator method applied to CH+ (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2112-2118 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new approach to the direct evaluation of excitation energies and transition moments from the polarization propagator is presented. The method, which uses a coupled cluster doubles (CCD) reference state within the framework of perturbative propagator methods, is applied to the lowest singlet and triplet excitations in CH+. Comparison of the coupled cluster doubles polarization propagator approximation (CCDPPA) results with experiments and standard perturbative polarization propagator calculations shows that a significant improvement is obtained with a coupled cluster rather than a Rayleigh–Schrödinger reference state: the singlet excitation energy is improved by about 0.5 eV and the triplet instability of the standard second order approach is removed. The radiative lifetime of the v'=0 level of the A 1Π state is estimated to be very close to 800 ns. The improved performance of the coupled cluster propagator method over propagator calculations based on Rayleigh–Schrödinger expansion mainly stems from a enhancement of the correlation coefficients for the lower double excitations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451156
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  • 9
    Electronic Resource
    Electronic Resource
    The calculated electronic excitation spectra of Si2C and Si3 (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 354-360 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The results of second order polarization propagator calculations of the valence excitation energies and oscillator strengths of Si2C and Si3 are reported and compared to the previously published spectrum of SiC2. The character and properties of the excitations are explored and suggestions are made as to excitations which may be amendable to experimental study. A previously observed optical transition in Si clusters is assigned to an intense line in the Si3 spectrum at about 46 000 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450829
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  • 10
    Electronic Resource
    Electronic Resource
    Excitation energy of linear propargylium (C3H3+). Can this ion be detected by laser-induced fluorescence in flames? (1984)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 88 (1984), S. 3121-3123 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j150658a040
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