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  • American Institute of Physics (AIP)  (17)
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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
    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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  • 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
    Direct atomic-orbital-based time-dependent Hartree–Fock calculations of frequency-dependent polarizabilities (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2978-2987 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have formulated and implemented a direct atomic integral driven method for the calculation of frequency-dependent response properties at the self-consistent-field level. By avoiding the integral transformation step, as well as the storing and retrieving of atomic-orbital-based integrals, we are able to use large basis sets. The practicality of the approach is illustrated and calibrated by performing a series of calculations on cyclopropenone employing up to 232 basis orbitals. We examined the scaling of the dipole polarizability (α) with the size of the system for paranitroaniline and its dimer. Except for a small positive enhancement of the component along the molecular axis, we find little effect of size on α for this system. However, if the –NN– linkage of the dimer is replaced by a –CC– linkage, thus more effectively extending the π-orbital conjugation by making the dimer planar, we find a large, frequency-dependent increase in the polarizability relative to twice that of the monomer (factors varying from 3 to 18, depending on frequency). This makes the –CC– linked polymer a potential candidate for achieving nonlinear chain length dependence of properties that depend on α.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461995
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  • 5
    Electronic Resource
    Electronic Resource
    Relativistic corrections to molecular dynamic dipole polarizabilities (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 2983-2990 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using response function methods we report calculations of the dynamic isotropic polarizability of SnH4 and PbH4 and of the relativistic corrections to it in the random phase approximation and at the correlated multiconfigurational linear response level of approximation. All relativistic corrections obtained from the use of the Darwin and mass-velocity operators to first order are included at both levels of approximation. We find that correlation and relativistic contributions are not even approximately additive for the two molecules. The importance of the relativistic corrections is smallest in the correlated calculations, as has also been observed for other properties. For SnH4 the correlation contribution and the pure relativistic correction are of the same order of magnitude, whereas for PbH4 the relativistic correction becomes more important than the correlation contribution. We report estimated Cauchy moments, obtained from fitting the dispersion of the calculated corrections as a function of ω2. The frequency dependence of the nonrelativistic polarizability is most pronounced at the correlated level, mainly due to lower excitation energies in the multiconfigurational calculations than those in the random phase approximation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470486
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Effects of the order of the energy asymptotes on the calculations of nuclear magnetic shieldings and static polarizabilities (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 10775-10782 
    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 nuclear magnetic shielding constants and static polarizabilities of CO, N2, F2, and CH4 in order to investigate the effect of decreasing the order (in perturbation theory) of the poles of the propagator, i.e., the energy asymptotes, but still requiring that all response terms to second order must be included. Our results show that the higher than second-order contributions from the poles are of vital importance for the nuclear magnetic shieldings and of less, but not negligible, importance for the static polarizabilities. As the order of the poles is decreased the SOPPA isotropic shieldings approach the results obtained within second-order perturbation theory (MP2), especially for CO, N2, and F2. This behavior is not as pronounced for the C shielding of CH4 and for polarizabilities. For the shieldings we obtain the best agreement with MP2 (and experiments) when the poles are calculated as Hartree–Fock energy differences using frozen ground state orbitals, and for the polarizabilities when the poles are calculated in the random phase approximation and Tamm–Dancoff approximation. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467890
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    A new implementation of the second-order polarization propagator approximation (SOPPA): The excitation spectra of benzene and naphthalene (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 5886-5900 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new implementation of the second-order polarization propagator approximation (SOPPA) using a direct linear transformation approach, in which the SOPPA equations are solved iteratively. This approach has two important advantages over its predecessors. First, the direct linear transformation allows for more efficient calculations for large two particle–two hole excitation manifolds. Second, the operation count for SOPPA is lowered by one order, to N5. As an application of the new implementation, we calculate the excitation energies and oscillator strengths of the lowest singlet and triplet transitions for benzene and naphthalene. The results compare well with experiment and CASPT2 values, calculated with identical basis sets and molecular geometries. This indicates that SOPPA can provide reliable values for excitation energies and response properties for relatively large molecular systems. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472430
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  • 10
    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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