Summary
A generalized Brillouin-Wigner equation for the firstM levels of a HamiltonianH=H 0+gV is derived. For positive interactionsgV>0 the Lippmann-Schwinger matrix functionals provide upper and lower bounds to these levels; the stationary values are related to the matrix Padé approximants when the Cini-Fubini ansatz is used. Numerical examples show that the [0/1] matrix Padé approximant gives a lower bound as accurate as the corresponding Rayleigh-Ritz upper bound when the same trial functions are used.
Riassunto
Si deriva un'equazione di Brillonin-Wigner generalizzata per i primiM livelli di un hamiltonianaH=H 0+gV. Per interazioni positivegV>0 i funzionali matriciali di Lippmann-Schwinger forniscono stime per eccesso e per difetto a questi livelli; i valori stazionari sono connessi agli approssimanti di Padé quando si usa l'ansatz di Cini-Fubini. Esempi numerici mostrano che l'approssimante matriciale [0/1] di Padé dà una stima per difetto accurata come la corrispondente stima per eccesso di Rayleigh-Ritz ottenuta usando lo stesso numero di funzioni di prova.
Резюме
Выводится обобщенное уравнение Бриллюэна-Вигнера для первыхM уровней ГамильтонианаH=H 0+gV. Для положительных взаимодействийgV>0 функционалы матрицы Липпмана-Швингера дают верхние и нижние границы зтих уровней. Стационарные значения связаны с матричным Падэ приближением, когда используется подход Чини-Фубини. Численные примеры показывают, что [0/1] матричное Падэ приближение дает нижнюю границу, а приближение Релея-Ритца—верхную границу, когда используются те же пробные функции.
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Work partially supported by Istituto Nazionale di Fisica Nucleare, Sezione di Bologna.
Перевебено ребакцйей.
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Turchetti, G., Ortolani, F. & Sagretti, C. Variational bounds to the excited states from a generalized Brillouin-Wigner equation. Nuov Cim A 44, 211–229 (1978). https://doi.org/10.1007/BF02813393
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DOI: https://doi.org/10.1007/BF02813393