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research article
Effective-State Approach to 2nd-Order Perturbation-Theory
1992
We show that the complete set of intermediate states in second-order perturbation expressions can be replaced by a finite number of states, provided the subspace they span contains one effective state, solution of an inhomogeneous equation. It is therefore not necessary that the subspace be complete. The existence of this effective state guides the choice of the basis in approximate calculations. As an example, we apply these considerations to two-photon transition rates in hydrogen.
Type
research article
Web of Science ID
WOS:A1992GX26400002
Authors
Publication date
1992
Published in
Volume
17
Issue
5
Start page
387
End page
392
Peer reviewed
REVIEWED
EPFL units
Available on Infoscience
October 8, 2009
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