The selection of which configurations to include in a
configuration interaction (CI) wavefunction is a compromise
between accuracy and computational difficulty. A compact
and accurate configuration interaction wavefunction can be
constructed by inclusion of all single and double
excitations and certain triple and quadruple excitations
chosen in an *a priori* manner according to how many
electrons are placed in several subsets of orbitals. Such a
wavefunction, denoted CISD[TQ], has previously been shown
to recover a large fraction of the energy of a CI
wavefunction including all single, double, triple, and
quadruple excitations (CISDTQ). A comparison of the
molecular geometry and harmonic vibrational frequencies of
hydrogen sulfide (H_{2}S) predicted by two CISD[TQ]
wavefunctions and the complete CISDTQ wavefunction are
presented. With the largest basis set used, a triple-zeta
plus double polarization basis with an additional set of
d-type functions added to hydrogen, and an additional set
of f-type functions added to sulfur [TZ2P(f,d)], the
CISD[TQ] predictions differ from the CISDTQ by 0.0003 Ang
in the bond length and by 0.02^{o} in the bond
angle. The CISD[TQ] harmonic vibrational frequencies differ
by less than 2 cm^{-1} from the full CISDTQ
predictions. These results suggest that the CISD[TQ]
wavefunction is an efficient and accurate truncation of the
complete CISDTQ and are particularly impressive considering
that with a TZ2P(f,d) basis, the larger CISD[TQ]
wavefunctions included roughly 300,000 configurations while
the CISDTQ includes almost nine million.