Spectacular Role of Electron Correlation in the Hyperfine Interactions   in $^2D_{5/2}$ States in Alkaline Earth Ions
  The low-lying n(=3,4,5)d $^2D_{5/2}$ states alkaline earth ions are of vital importance in a number of different physical applications. The hyperfine structure constants of these states are characterized by unusually strong electron correlation effects. Relativistic coupled-cluster theory has been employed to carry out {\it ab initio} calculations of these constants. The role of the all order core-polarization effects was found to be decisive in obtaining good agreement of the results of our calculations with accurate measurements. The present work is an apt demonstration of the power of the coupled-cluster method to cope with strongly interacting configurations. 
B. K. Sahoo, C. Sur, T. Beier, B. P. Das, R. K. Chaudhuri and D.   Mukherjee