A simple coupling scheme between nonlocal Hartree−Fock exchange,
gradient corrected local spin-density
exchange, and the Pade approximated Vosko, Wilk, and Nusair correlation
functional is reported. The
combination of these functionals with the electrons kinetic and Coulomb
repulsion terms yields a method
that scales as ∼N
3, where N is the
number of basis functions, compared to ∼N
7 for
Gaussian-2 (G2) ab initio
theory and ∼N
4 and
∼N
5 for Becke's B3LYP and Bx88/Bc95 density
functional approaches. The reported
method is denoted by HFS−BVWN, which stands for
Hartree−Fock−Slater−Becke−Vosko−Wilk−Nusair.
The results of HFS−BVWN/6-311+g(3df, p) computations on
atoms of the first two rows of the periodic
table, hydrogen−argon, and selected small molecules showed that the
method underestimates atomic and
molecular exchange-correlation (XC) energies by ∼ 0.13% and 0.14%,
respectively. We demonstrated that
the application of Dewar's atom equivalent scheme to atomic energies
partially compensated for the errors
in XC energies. Atom equivalents for hydrogen through chlorine,
excluding the noble gases, were derived.
In a data set comprised of 150 atomic and molecular species, the
reported method achieved average absolute
errors of 1.8 kcal/mol and 0.12 and 0.13 eV for room temperature heats
of formation, ionization potentials,
and electron affinities, respectively. The overall average
absolute error of HFS−BVWN method, 2.5 kcal/mol, is thus within 0.5 kcal/mol from the corresponding accuracies of G2
and Bx88/Bc95 theories, 2 kcal/mol, and superior to the B3LYP (3.5 kcal/mol) and BLYP (3.9 kcal/mol)
methods. The HFS−BVWN/6-311+g(3df, p) level of theory is much less computer intensive
than the G2, B3LYP, and Bx88/Bc95 theories
and, thus, may be applicable to larger molecular systems than those
attainable by the latter approaches.
