  The interactions of charm and bottom quarks in a Quark-Gluon Plasma (QGP) are
evaluated using a thermodynamic 2-body T-matrix. We specifically focus on
heavy-quark (HQ) interactions with thermal gluons with an input potential
motivated by lattice-QCD computations of the HQ free energy. The latter is
implemented into a field-theoretic ansatz for color-Coulomb and (remnants of)
confining interactions. This, in particular, enables to discuss corrections to
the potential approach, specifically hard-thermal-loop corrections to the
vertices, relativistic corrections deduced from pertinent Feynman diagrams, and
a suitable projection on transverse thermal gluons. The resulting potentials
are applied to compute scattering amplitudes in different color channels and
utilized for a calculation of the corresponding HQ drag coefficient in the QGP.
A factor of ~2-3 enhancement over perturbative results is obtained, mainly
driven by the resummation in the attractive color-channels.
