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Perturbation Theory for Degenerate Problems of Many-Fermion Systems

Journal Article · · Progress of Theoretical Physics (Kyoto)
DOI:https://doi.org/10.1143/PTP.29.351· OSTI ID:4683966
The linked cluster expansion of the eigenvalues and eigenfunctions of a many-fermion system is extended to the case where the eigenvalues of the unperturbed system are degenerate. It is shown that the eigenvalues and eigenfunctions are to be obtained by solving a secular equation in the space of degenerate unperturbed wave functions; the matrix elements between these unperturbed functions take the form of linked clusters with energy denominators that are the differences of unperturbed energies. Some discussions are given on the relation of this theory to the formalism of Bloch and Horowitz, in which the energy denominators are the differences of an unperturbed energy and the true energy that is to be obtained as the solution to the secular equation.
Research Organization:
SHizuoka Univ., Japan
Sponsoring Organization:
USDOE
NSA Number:
NSA-17-024348
OSTI ID:
4683966
Journal Information:
Progress of Theoretical Physics (Kyoto), Journal Name: Progress of Theoretical Physics (Kyoto) Journal Issue: 3 Vol. 29; ISSN 0033-068X
Country of Publication:
Country unknown/Code not available
Language:
English

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