Note on the choice of basis set in density functional theory calculations for electronic structures of molecules (test on the atoms from the first three rows of the periodic table (2 ⩽ N ⩽ Z ⩽ 18), water, ammonia and pyrrole)

The effect of basis set in Kohn-Sham theory on estimating correlation energy was investigated using a density functional subroutine and a Hartree-Fock SCF one-electron density program (working with arbitrary basis set). Lee-Yang-Parr density functional estimation, MP2 perturbation calculation and Davidsonʹs accurate configuration interactions calculations for correlation energies of atoms were used for this test. In the density functional estimation a simple 3-21G basis set has produced the same results as the huge triple-zeta basis set with polarization functions within the chemical accuracy (1 kcal/mol).