Table-configuration interaction method

Table 10.20. Potential curves (in Hartrees) for the five lowest electronic states of CH, calculated by Lie, Hinze and Liu [188] using an extended configuration interaction method...

As the above narrative indicates, most of the ideas for the treatment of the many-electron problem were first developed by the nuclear and solid-state physicists. This is the case not only for perturbative methods, but also for variational ones, including the configuration interaction method, which nuclear physicists refer to as the shell model, or for the unitary group approach (see Ref. [90] for additional references see Refs. [23, 78-80]). The same applies to the CC approach [70]. For this reason, quantum chemists, who were involved in the development of post-Hartree-Fock methods, paid a close attention to these works. However, with Cizek s 1966 paper the tables were turned around, at least as far as the CC method is concerned, since a similar development of the explicit CC equations, due to Liihrmann and Kiimmel [91] had to wait till 1972, without noticing that by that time quantum chemists were busily trying to apply these equations in actual computations. 

Table 11 Vertical excitation energies (in eV) for N2. KS and HF denote limited configuration-interaction calculations based on either the Kohn—Sham (KS) or Hartree-Fock (HF) orbitals, whereas CCSD and SOPPA represent results of sophisticated configuration-interaction methods. The final state and the electronic excitation are also shown and the results are compared with experimental values (Exp.). The results are from ref. 84...

The augmented correlation consistent basis sets, when combined with coupled cluster or multireference configuration interaction methods, have been found to provide an accurate description of atomic electron affinities. The calculated EAs of boron and fluorine are summarized in Table 26 and the basis set convergence errors are plotted in Figure 13. The values of the EAs of these two atoms, 6.39 0.23 kcal mol (B) and 78.82 kcal mol" (F), respectively (corrected for spin-orbit effects), bracket the EAs of the other first-row atoms. 

One observation made by Ludena for the confined He atom is that the CE, obtained with the configuration interaction method, is almost constant when the helium atom is confined. From Table 3, it is clear that with the MP2 method this result is preserved. Comparing the with the CE obtained by Ludena, it is observed that the MP2 method recover at least the 90% of the correlation energy for any confinement radii. 

The ideal calculation would use an infinite basis set and encompass complete incorporation of electron correlation (full configuration interaction). Since this is not feasible in practice, a number of compound methods have been introduced which attempt to approach this limit through additivity and/or extrapolation procedures. Such methods (e.g. G3 [14], CBS-Q [15] and Wl [16]) make it possible to approximate results with a more complete incorporation of electron correlation and a larger basis set than might be accessible from direct calculations. Table 6.1 presents the principal features of a selection of these methods. 

In table 2 our result is compared with the UV spectroscopic result of Klein et al. [26], Also shown are the theoretical results of Zhang et al. [2], Plante et al. [27], and Chen et al. [28], The first of these uses perturbation theory, with matrix elements of effective operators derived from the Bethe-Salpeter equation, evaluated with high precision solutions of the non-relativistic Schrodinger equation. This yields a power series in a and In a. The calculations of Zhang et al. include terms up to O(o5 hi a) but omit terms of 0(ary) a.u. The calculations of Plante et al. use an all orders relativistic perturbation theory method, while those of Chen et al. use relativistic configuration interaction theory. These both obtain all structure terms, up to (Za)4 a.u., and use explicit QED corrections from Drake [29],... 

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