Polarization propagator second-order

We have employed the second-order polarization propagator approximation (SOPPA) in this study, a method which was mainly developed by Jens Oddershede and his co-workers [3,4,20,51-56]. Barone et al. [32] have recently shown that SOPPA reproduces the vicinal F-F couplings reasonably well in 1,2-difluoroethene. 

SOPPA second order polarization propagator approach... 

The second-order polarization propagator approximation (see Section VII. D). 

The resulting second-order polarization propagator approximation (SOPPA) was first described in its present form by Nielsen et al. (1980). Splitting h4 up into 2p-2h and 2h-2p excitation operators as was done for h2 in Eqs (95)-(97)... 

The second-order polarization propagator approximation is closely related to the equation-of-motion (EOM) method (McCurdy et al., 1977). The equations that determine the excitation energies are the same up through the... 

S.P.A. Sauer, G.H.F. Diercksen, J. Oddershede, Second Order Polarization Propagator Calculations of Dynamic Polarizabilities and Cs Coefficients, Int. 1. Quantum Chem. 39 (1991) 667. 

The static and dynamic polarizability of the polyyne (C2 H2) series is treated in the TDHF and correlated second order polarization propagator methods by Dalskov et al.2i2 The calculated polarizabilities are extrapolated to the infinitely... 

For a polyyne chain142 the static al and dynamic a(— co)L polarizabilities have been computed using non-linear sequence transformations for the extrapolation and besides RPA the SOPPA (correlated second order polarization propagator approximation) method. In this way the authors have obtained for a C2 iH2 (polyyne) chain quite stable extrapolated values for both quantities. 

There do exist recent quantum chemical techniques which are size consistent. Among them, the Random Phase Approximation (RPA), its variants such as the Second-Order Polarization Propagator Approximation (SOPPA) [10], and the Coupled Cluster Approximation (CCA) [11] axe the most prominent and being widely used. In the SOPPA method, electron correlation effects are included in the two-particle polarization propagator to second order. The coupled cluster method uses an exponential ansatz through which higher-order exci-... 

In this substection we will shortly discuss the computational methods used for calculation of the spin-spin coupling constants. Two main approaches available are ab initio theory from Hartree-Fock (or self-consistent field SCF) technique to its correlated extensions, and density function theory (DFT), where the electron density, instead of the wave function, is the fundamental quantity. The discussion here is limited to the methods actually used for calculation of the intermolecular spin-spin coupling constants, i. e. multiconfigurational self consistent field (MCSCF) theory, coupled cluster (CC) theory and density functional theory (DFT). For example, the second order polarization propagator method (SOPPA) approach is not... 

By the end of the 1980s, state of the art methods of quantum chemistry, such as coupled cluster, configuration interaction, fourth order perturbation theory (MP4), second-order polarization propagator (SOPPA, multiconfigu-rational linear response (MCLR) etc., had been applied to the calculation of... 

Empirical equilibrium coupling constants can be compared as a benchmark with calculated equilibrium coupling constants obtained with various methods. A comparison of these empirical equilibrium constants with calculated equilibrium constants suggested that the restricted-active-space self-consistent field (RASSCF) method is the best approach for calculating the indirect nuclear spin-spin coupling constants of small molecules, and that the second-order polarization propagator approximation (SOPPA) and DFT are similar in performance. 

Second-Order Polarization Propagator Approximation Calculations. -... 

SLITDRESS slice interleaved depth resolved surface coil spectroscopy SOPPA second order polarization propagator approach... 

The paramagnetic contribution is more demanding to calculate and is a bit more sensitive to electron correlation, although not a great deal. For instance, for ammonia, the RPA (effectively uncorrelated) value is 38.45 ppm a.u., while the Second Order Polarization Propagator Approximation (correlated) yields 38.15 ppm a.u. 

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