Contracted Gaussian-type function sets are developed for correlating functions of the ten main group elements from Cs to Ra. A segmented contraction scheme is used for its compactness and efficiency. Contraction coefficients and exponents are determined by minimizing the deviation from accurate natural orbitals or K-orbitals, incorporating the relativistic effect by the third-order Douglas-Kroll approximation. The present basis sets yield more than 98% of atomic correlation energies predicted by accurate natural orbitals of the same size. The use of the present set with the model core potential methods gives more than 99% of the correlation energies obtained by the atomic natural orbitals optimized for the model core potential itself. The present correlating sets applied to relativistic model core potential methods including spin-orbit effects predict the spectroscopic constants of the BiH molecule in excellent agreement with experimental results. (C) 2003 American Institute of Physics.