We show that an economic basis set can describe systems involving sodium-organic interaction in ab initio calculations. Basis sets, in which the polarization and the diffuse functions are considered only for sodium and atoms of strong electronegativity of various Na-containing weakly bound systems, can predict geometric structures, dipole moments and binding energies with negligible basis set superposition error (BSSE), comparable to those using 6-31+G* in calculations with density functional theory. This study is expected to provide a general guideline for basis set selection in computations of large systems involving metal-organic interaction.