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Application of graphical methods of spin algebras to limited CI approaches. I. Closed shell case
Author(s) -
Paldus J.,
Adams B. G.,
Čížek J.
Publication year - 1977
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560110511
Subject(s) - diagrammatic reasoning , feynman diagram , excited state , open shell , second quantization , quantization (signal processing) , spin (aerodynamics) , physics , coupling (piping) , symmetry (geometry) , identical particles , quantum mechanics , quantum , matrix (chemical analysis) , theoretical physics , mathematics , chemistry , computer science , geometry , materials science , algorithm , creation and annihilation operators , chromatography , metallurgy , thermodynamics , programming language
The time independent diagrammatic technique based on the mathematical methods of quantum electrodynamics (second quantization, Wick's theorem, Feynman‐like diagrams) is combined with graphical techniques of spin algebras to derive general expressions for the matrix elements of spin independent one‐ and two‐particle operators between spin symmetry adapted ground, mono‐ and bi‐excited configurations of a closed shell system. Two coupling schemes are considered for bi‐excited states and their relative merits are discussed. Finally, the results are used to derive compact expressions for the coupling coefficients of the direct configuration interaction from molecular integrals ( CIMI ) method.