  Dipole moments are a simple, global measure of the accuracy of the electron
density of a polar molecule. Dipole moments also affect the interactions of a
molecule with other molecules as well as electric fields. To directly assess
the accuracy of modern density functionals for calculating dipole moments, we
have developed a database of 200 benchmark dipole moments, using coupled
cluster theory through triple excitations, extrapolated to the complete basis
set limit. This new database is used to assess the performance of 88 popular or
recently developed density functionals. The results suggest that double hybrid
functionals perform the best, yielding dipole moments within about 3.6-4.5%
regularized RMS error versus the reference values---which is not very different
from the 4% regularized RMS error produced by coupled cluster singles and
doubles. Many hybrid functionals also perform quite well, generating
regularized RMS errors in the 5-6% range. Some functionals however exhibit
large outliers and local functionals in general perform less well than hybrids
or double hybrids.
