The Brueckner-Goldstone many-body perturbation method, previously utilized for calculations of atomic correlation energies and polarizabilities, has been extended to the study of the hyperfine structure. The correlation energy as well as the hyperfine coupling constant of the lithium atom are calculated and compared with the results of some earlier methods. The present method makes use of Feynman-like diagrams which facilitate the evaluation of the importance of various physical effects. Analysis of the hyperfine diagrams shows that the difference between the experimental and the Hartree-Fock values is mainly accounted for by spin polarization, although correlation effects are by no means negligible. Our result of 2.887 a. u. agrees very well with the experimental value of 2.9096 a. u. The excellent result for the total energy of -7.478 a. u., comparing with the corresponding experimental value of -7.47807 a. u., shows that the wave function is good over-all, as well as in the region near the nucleus.

• Received 9 October 1967

DOI:https://doi.org/10.1103/PhysRev.174.1