Systematic study of basis set superposition errors in the calculated interaction energy of two HF molecules.

We have calculated the interaction energy of two HF molecules at the single-configuration Hartree–Fock level using 34 different basis sets in an effort to assess the reliability and usefulness of the counterpoise correction to account for basis set incompleteness. We find large counterpoise corrections for all configurations studied, and we show that using a large enough basis set so that the counterpoise correction is small does not guarantee accurate results. Furthermore even for smaller basis sets the inclusion of counterpoise corrections does not systematically improve the accuracy of the calculations. [ABSTRACT FROM AUTHOR]