Accurate small split-valence 3-21SP and 4-22SP basis sets for the first-row atoms

Split-valence Gaussian 3-21SP and 4-22SP basis sets are presented for the ground states of the first-row elements of the Periodic Table. The total energies of the atoms calculated with the new basis sets are significantly lower than those obtained with the well-known 3-21G and 4-31G basis sets. This is the consequence of the fact that the 3-21G and 4-31G basis sets do not correspond to the global minimum of the energy functional in the Hartree-Fock approximation. It is also shown that the 4–22 contraction scheme better corresponds to the solution structure of the Hartree-Fock equations with uncontracted 8s4p basis sets, and therefore permits one to obtain lower total energies than with the 4–31 contraction scheme. The proposed basis sets are tested by performing geometry optimizations and calculating the normal frequencies for the LiH, BeH2, BH3, CH4, NH3, OH2, and FH molecules within the Hartree-Fock approximation.