Abstract This paper studies the two-vibron bound states in the $\beta $--Fermi--Pasta--Ulam model by means of the number conserving approximation combined with the number state method. The results indicate that on-site, adjacent-site and mixed two-vibron bound states may exist in the model. Specially, wave number has a significant effect on such bound states, which may be considered as the quantum effects of the localized states in quantum systems.
Received: 14 February 2008
Revised: 24 April 2008
Accepted manuscript online:
PACS:
63.20.D-
(Phonon states and bands, normal modes, and phonon dispersion)
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