Title Extension of an efficient approach for spin-angular integrations in atomic structure calculations
Authors Gaigalas, Gediminas
DOI 10.3390/atoms14030021
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Is Part of Atoms.. Basel : MDPI. 2026, vol. 14, iss. 3, art. no. 21, p. 1-27.. ISSN 2218-2004
Keywords [eng] complex atom ; configuration interaction ; energy level ; LS-coupling ; matrix element ; quasi-spin ; Racah algebra ; recoupling coefficients ; reduced matrix element ; completely reduced matrix ; second quantization ; spin-angular integration ; tensor operators ; theoretical methods
Abstract [eng] In this study, an extension of the general method [G. Gaigalas, Z. Rudzikas, C. Froese Fischer, J. Phys. B, At. Mol. Phys. (1997). DOI: 10.1088/0953-4075/30/17/006] is described for finding algebraic expressions of the spin-angular parts of the reduced matrix elements of any one- and two-particle operator for an arbitrary number of shells in an atomic configuration. This extension is related, at first, to a change in the definition of tensor structure, where a non-scalar space with respect to l and s for any two-particle operator acts on four different shells. This leads to more efficient expressions for recoupling matrices and amplitudes, which are presented in the paper. In addition, the paper presents new expressions for some of the recoupling matrices, in which 6j- and 9j-coefficients are summed up algebraically. All this leads to a significantly simpler and faster calculation of the spin-angular parts of any non-scalar two-particle operator.
Published Basel : MDPI
Type Journal article
Language English
Publication date 2026
CC license CC license description