The geometries and chemical structures of lithium- and copper-passivated substitutional B in crystalline Si are calculated and compared to the ones of hydrogen-passivated B. The calculations are done at the approximate ab initio several clusters. In contrast to H which bridges an acceptor-Si bond and forms a stronger bond with Si than with the acceptor, Li and Cu are at the antibonding site to the boron atom, and form Li-B and Cu-B bonds. Their wave functions overlap with several host atoms. The results show that copper is a viable candidate as the observed passivator X.