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On the use of spin graphs for spin adapting many‐body perturbation theory
Author(s) -
Mukhopadhyay Atri
Publication year - 1984
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.560250605
Subject(s) - perturbation theory (quantum mechanics) , perturbation (astronomy) , spin (aerodynamics) , physics , generalization , theoretical physics , ground state , excitation , statistical physics , quantum mechanics , mathematics , mathematical analysis , thermodynamics
Abstract In connection with spin adaptation in many‐body perturbation theory, this paper reexamines the use of spin graphs in view of a Hugenholtz‐like representation where both the orbital and the spin parts coexist. Together with the idea of essentially distinct diagrams, this representation leads to an economic handling of spin adaptation. As a side issue, the appropriate generalization of the Epstein–Nesbet partitioning for spin‐adapted perturbation theory is obtained. Compact formulas up to fourth order of the ground‐state energy, and up to third order for excitation energies and ionization potentials are given.