Configuration-interaction theory

Mies FH (1968) Configuration interaction theory, effects of overlapping resonances. Phys Rev 175 164... 

The advances in this field are related with the development of the theory of configuration interaction between different excitation channels in nuclear physics including quantum superposition of states corresponding to different spatial locations for interpretation of resonances in nuclear scattering cross-section [7] related with the Fano configuration interaction theory for autoionization processes in atomic physics [8],... 

If you don t understand the above equation and its exegesis, recall Eq. 5.169 (there c was used for a, the weighting, when squared, of the CSF/determinant in the total wavefunction). That equation shows how in configuration interaction theory (CASSCF is a version of Cl) each electronic state, ground, first excited, etc., has a total wavefunction T which is a linear combination of determinants (or CSFs, for open-shell species). Within each D, for example the determinant of Eq. 5.167, we have a number of MOs i//. 

As of 1994 the configuration interaction theory of Ohtsuki [5] and the molecular theory of Shimamura [6] played important guiding roles for experimentalists in their study of the peculiar phenomena of the p longevity. After 1995 more sophisticated theoretical methods have been developed. These overcome the intrinsic limitation of treating the pHe+ system in adiabatic approximation by covering the molecular aspects and the configuration interaction aspects equally well. 

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],... 

Full-scale treatments of correlation effects, found to be necessary to repair some of the known deficiencies of the HF model wavefunction, generally are done by Configuration Interaction theory [l),(5j. With highly developed computer codes it has been found possible to include more than 10s — 10 determinants, either explicitly or implicitly in the wavefunction expansion. Unfortunately, procedures for selecting the most important terms in the Cl expansion have proved to be a source of difficulty, despite successes of Coupled Cluster methods and related schemes (6],[7]. 

These many-body theories utilize an altogether different operator basis, the many-body basis. These basis operators account for correlation in an approximate way, since they act on the correlation part of the ground state as well as the SCF term. Hence, the many-body basis operators have interesting physical interpretations as primitive ionization or excitation operators. In addition to the excitation operators, the complete many-body basis set for excitation energies includes primitive de-excitation operators, which have no analogs in traditional configuration interaction theory. The many-body basis for ionization processes includes operators that remove electrons from particle orbitals. These operators are also without simple counterparts in Cl theory. The various terms in the expression for photoionization cross sections have been analyzed in light of the physical content of the many-body basis set. 

QCISD, QCISDT quadratic configurational interaction theory... 

Real energy hermitian approaches. Extension of Fano s K-matrix, configuration interaction theory... 

D.E. Ramaker, D.M. Schrader, Multichannel configuration-interaction theory Application to some resonances in Helium, Phys. Rev. A 9 (1980) 1974. 

Hence the approximation (1), which is a prototype of multistructure valence bond theory, is equivalent to approximation (4), a prototype of molecular orbital configuration interaction theory, and both (1) and (4) are equivalent to (13), the Coulson-Fischer wave function. 

H. Nakatsuji, J. Chem. Phys., 94, 6716 (1991). Exponentially Generated Configuration Interaction Theory. Descriptions of Excited, Ionized, and Electron Attached States. 

Z. He and D. Cremer, Int. J. Quantum Chem., Quant. Chem. Symp., 25,43 (1991). Analysis of Coupled Cluster and Quadratic Configuration Interaction Theory in Terms of Sixth-Order Perturbation Theory. Z. He and D. Cremer, Theor. Chim. Acta, 85, 305 (1993). Analysis of Coupled Cluster Methods. 11. What Is the Best Way to Account for Triple Excitation in Coupled Cluster Theory. ... 

Z. He and D. Cremer, Int. J. Quantum Chem., Quantum Chem. Symp, 25, 43 (1991). Analysis of Coupled Cluster and Quadratic Configuration Interaction Theory in Terms of Sixth-Order Perturbation Theory. 

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