Relativistic coupled-cluster theory of nuclear spin-dependent parity   non-conservation
  We have developed a relativistic coupled-cluster theory to incorporate nuclear spin-dependent interaction Hamiltonians perturbatively. In this theory, the coupled-cluster operators in the electronic sector are defined as tensor operators of rank one and we introduce suitable diagrammatic representations. For properties calculations, the electronic part is first calculated and later coupled to the nuclear spin part. The method is ideal to calculate parity violating nuclear spin-dependent electric dipole transition amplitudes, $E1_{\rm PNC}^{\rm NSD}$, of heavy atoms. To validate the proposed method the $E1_{\rm PNC}^{\rm NSD}$ of the transition $6\; ^2S_{1/2} \rightarrow 7\; ^2S_{1/2}$ in $^{133}$Cs is calculated for selected MBPT diagrams and compared with the results from our theory. 
B. K. Mani and D. Angom
physics.atom-ph