  The band structure of the novel low-temperature thermoelectric material,
\CBT, is calculated and analyzed using the semi-classic transport equations. It
is shown that to obtain a quantitative agreement with measured transport
properties a band gap of 0.08 eV must be enforced. A gap in reasonable
agreement with experiment was obtained using the generalized gradient
functional of Engel and Vosko. We found that the experimental $p$-type sample
has a carrier concentration close to optimal. Furthermore the conduction bands
have a form equally well suited for thermoelectric properties and we predict
that an optimally doped $n$-type compound could have thermoelectric properties
exceeding those of the $p$-type.
