  Density functional theory(DFT) and Hartree-Fock(HF) calculations are reported
for the family of transition metal fluorides $\mbox{ScF}_3$, $\mbox{TiF}_4$,
$\mbox{VF}_5$, and $\mbox{CrF}_6$. Both HF and the local-density-aproximation
(LDA) yield excellent agreement with experimental bond lengths, while the B-LYP
gradient-corrected density functional gives bond lengths $0.04-0.05$ \AA\ too
long. An investigation of various combinations of exchange and correlation
functionals shows that, for this series, the origin of this behavior lies in
the Becke exchange functional. Much improved bond distances are found using the
hybrid HF/DFT functional advocated by Becke. This approximation also leads to
much improved thermochemistries. The LDA overestimates average bond energies in
this series by $30-40$ kcal/mol, whereas the B-LYP functional overbinds by only
$\sim8-12$ kcal/mol, and the hybrid HF/DFT method overbinds by only $\sim 2$
kcal/mol. The hybrid method predicts the octahedral isomer of $\mbox{CrF}_6$ to
be more stable than the trigonal prismatic form by $14$ kcal/mol. Comparison of
theoretical vibrational frequencies with experiment supports the assignment of
an octahedral geometry.
