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Alternative perturbation method for the molecular vibration–rotation problem
Author(s) -
CassamChenaï P.,
Liévin J.
Publication year - 2003
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.10556
Subject(s) - hamiltonian (control theory) , ab initio , scaling , perturbation (astronomy) , vibration , perturbation theory (quantum mechanics) , quantum , physics , chemistry , quantum mechanics , mathematics , geometry , mathematical optimization
This article introduces an alternative perturbation scheme to find approximate solutions of the spectral problem for the rotation–vibration molecular Hamiltonian. The method is implemented for the Watson Hamiltonian and applied to methane. The complete J = 0 spectrum of this penta‐atomic molecule of atmospheric interest is calculated up to 9200 cm −1 in a purely ab initio fashion. Then, the rotational spectra of the vibrational ground state is obtained up to J = 18. The largest relative error is 2.10 −5 (for the highest J = 18 level) after scaling of a single parameter. Without scaling the accuracy on the rotational levels is limited by that of the ab initio equilibrium bond distance. The convergence of our results is analyzed with respect to the different parameters involved in our approach. The important concept of vibrational mean‐field configuration interaction is introduced. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 245–264, 2003