Relativistic calculations of core-polarisation effects on the hyperfine structure in the alkalis

A method for relativistic calculations of the hyperfine structure in the alkalis including core-polarisation effects is presented. The infinite summations over excited states is performed by using the inhomogeneous differential equation technique. By solving the equations recursively, the core-polarisation effects can be included to all orders. The relation of this method to the Unrestricted Dirac-Fock approach and to the method used by Das and co-workers is discussed and numerical results are presented for the ground states of the alkalis from Na to Fr. (Auth.)