ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Classical and quantum descriptions of proton vibration are compared for a coupled nonharmonic model based on an ab initio potential for the bifluoride ion, [FHF]−. Accurate quantum calculations and exact classical dynamics are compared with quantum and classical versions of the self-consistent-field (SCF) approximation. Semiclassical and quantum SCF eigenvalues agree within JWKB-type errors. The SCF scheme closely approximates exact quantum states for the lowest 4–5 vibrational levels of each symmetry, except at avoided crossings where strong CI mixing of SCF levels occurs. True classical motion, however, is mainly irregular except at very low energies, and even where it remains regular it may be strongly reorganized by a 1:1 periodic resonance associated with major potential surface features. Strongly mixed CI states at systematic avoided crossings of SCF levels at higher energies do have classical analogs in the reorganized classical motions seen at low energies; stabilized CI components correspond to a stable periodic 1:1 orbit, destabilized components to an unstable periodic 1:1 elliptical orbit. Canonical perturbation theory is used to study further the sense in which the exactly separable classical SCF Hamiltonian is "close'' to the true Hamiltonian. Where true motion is modal or SCF-like, first-order perturbed trajectories and second-order perturbed energies describe it very accurately. However since the dynamics can be strongly disturbed even at very low energies, correlation effects are obviously not "small'' in the sense usually meant in classical dynamics, i.e., that regular trajectories mostly remain regular in the nonseparable perturbed system.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.466060
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