1974/12/21 by Ingvar Lindgren, I Lindgren · 7 citations
Chemistry · Physics and Astronomy · #Atomic and Molecular Physics #Laser-Matter Interactions and Applications #Mass Spectrometry Techniques and Applications
paper · doi:10.1088/0022-3700/7/18/010
crossref issued 1974/12/21 · crossref published 1974/12/21 · crossref published-print 1974/12/21 · openalex publication_date 1974/12/21 · crossref published-online 2001/03/14 · crossref created 2002/07/26 · crossref deposited 2020/04/11 · openalex created_date 2025/10/10 · crossref indexed 2026/08/01 · openalex updated_date 2026/08/01
The Rayleigh-Schrodinger perturbation formalism is extended to the case of a model space, which is not necessarily degenerate. The model space defines the zero-order or model wavefunction, and the new formalism makes it possible to use a model wavefunction of multi-configurational type. The effect of the states outside the model space are taken into account by means of a perturbation expansion and expressed in terms of an 'effective' Hamiltonian, operating only within the model space. The extended Rayleigh Schrodinger formalism is used to prove the linked-diagram theorem for a multi-configurational model space in a simple way. The problem of convergence of the perturbation expansion is briefly discussed.