DFT(B3PW9I) calculations have been used to propose models for C5H5 (Cp) in lanthanides at a low computational cost. The H exchange reaction, Cp(2)LnH* + H-2 --> Cp(2)LnH + HH*, previously studied with C5H5 has been used as a benchmark. The Cp ligand has been replaced by H, by Cl, and also by an effective group potential (EGP). The three models give results close to that with C5H5 for the entire lanthanide series (La to Lu). As expected, the EGP gives the best agreement. Surprisingly, H gives better results than Cl. The electron donating ability (Cp closer to H than to Cl) is more important than isolobality (Cp and Cl).