  We extend the natural orbital impurity solver [PRB 90, 085102 (2014)] to
finite temperatures within the dynamical mean field theory and apply it to
calculate transport properties of correlated electrons. First, we benchmark our
method against the exact diagonalization result for small clusters, finding
that the natural orbital scheme works well not only for zero temperature but
for low finite temperatures. The method yields smooth and sufficiently accurate
spectra, which agree well with the results of the numerical renormalization
group. Using the smooth spectra, we calculate the electric conductivity and
Seebeck coefficient for the two-dimensional Hubbard model at low temperatures
which are in the scope of many experiments and practical applications. These
results demonstrate the usefulness of the natural orbital framework for
obtaining the real frequency information within the dynamical mean field
theory.
