Abstract: The relativistic pseudopotential ab initio calculation and the density fanctional theory(B3LYP)were separately used to perform the geometry optimizations for the cationic Rh(DIPHOS)(MAC)+ complex.The geometry optimized conformed perfectly to the data of x-ray diffraction in the different basis sets and methods.The results show these calculation methods can be used in the optimization of the larger intermediates including heavy metal.The B3LYP method can improve the geometry parameters in relationship with Rh.P-Rh bond lengths also are improved when increasing a d-polarization function to the basis set of P atoms.