On application of 0s orbitals in SCF calculations

The 0s orbitals, i.e., functions of the form [exp(−ar)−exp(−br)]/r, appear in the iterative solution of the Hartree–Fock equations. The inclusion of these functions in the basis set for the standard SCF calculation for helium is shown to give much better values for the SCF energy than those obtained by using the 1s functions alone, especially in smaller basis sets. This result is rather contradictory to a previous work of Zung and Parr. Using a five term basis set we have obtained the SCF energy of the He atom to be equal to −2.861 679 995 612 a.u. Our results indicate that the disagreement between the Roothaan–Soukup and Gazquez–Silverstone ’’SCF limits’’ for the He atom should be resolved in favor of the latter, which is identical with our result to all digits quoted. A routine use of the 0s functions in SCF calculations for atoms and molecules is advocated.

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