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Unitary transformation on the model space. Comparison of Brandow's and Kirtman's versions of quasidegenerate many body perturbation theory
Author(s) -
Svrček Michal,
Hubač Ivan
Publication year - 1987
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.560310408
Subject(s) - unitary transformation , unitary state , perturbation (astronomy) , perturbation theory (quantum mechanics) , operator (biology) , transformation (genetics) , mathematics , mathematical physics , physics , quantum mechanics , quantum , chemistry , biochemistry , repressor , political science , transcription factor , law , gene
In this paper we study the unitary transformations on the model space in quasidegenerate many body perturbation theory ( QDMBPT ). From this point of view we compare Brandow's and Kirtman's versions of QDMBPT up to the fifth order of perturbation expansion. We show that, starting from Brandow's QDMBPT , we can derive various versions of effective Hamiltonians order by order, of which the Kirtman's version is the simplest one. The operator of unitary transformation we express through the correlation operator.