Abstract
In this paper the authors describe a semi-empirical, approach for calculating certain high-order perturbation effects in a simple manner. They use these modified orbitals in RPA type equations to give values for E1 transition matrix elements and hyperfine dipole constants that agree well with experiment. Including the spin-independent weak interaction leads to parity non-conserving equations. For the caesium 6s12/ to 7s1/2 parity non-conserving E1 transition they obtain 0.904(1+or-0.02)*10-11 (-iea0Qw/N).