Geodesic
Algorithm of Rayleigh–Schrödinger perturbation theory for hermitian operators
Teoretičeskaâ i matematičeskaâ fizika, Tome 18 (1974) no. 3, pp. 374-382 
Yu. I. Polyakov. Algorithm of Rayleigh–Schrödinger perturbation theory for hermitian operators. Teoretičeskaâ i matematičeskaâ fizika, Tome 18 (1974) no. 3, pp. 374-382. http://geodesic.mathdoc.fr/item/TMF_1974_18_3_a8/
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     author = {Yu. I. Polyakov},
     title = {Algorithm of {Rayleigh{\textendash}Schr\"odinger} perturbation theory for hermitian operators},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {374--382},
     year = {1974},
     volume = {18},
     number = {3},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_1974_18_3_a8/}
}
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Voir la notice de l'article provenant de la source Math-Net.Ru

A simple algorithm of perturbation theory is obtained for an Hermitian operator $H=H^0+V$, where $V=A_1+A_2+\dots+A_n+\cdots$ and $A_n$ is an operator of $n$-th order with respect to a set of small parameters. The multiplicity of degeneracy of the unperturbed level is arbitrary. The scheme can be used, for example, in the problem of vibrational-rotational coupling in molecules. This is illustrated for the example of a triatomic linear symmetric molecule.

[1] L. D. Landau, E. M. Lifshits, Kvantovaya mekhanika, Fizmatgiz, 1963

[2] T. Kato, Teoriya vozmuschenii lineinykh operatorov, «Mir», 1972 | MR | Zbl

[3] A. S. Davydov, G. F. Filippov, “Vraschatelnaya energiya sistemy vzaimodeistvuyuschikh chastits”, Sb., posvyaschennyi akad. N. N. Bogolyubovu v svyazi s ego 60-letiem, «Nauka», 1969

[4] Yu. I. Polyakov, Opt. spektr., 33 (1972), 457