  Starting from the QCD Lagrangian and taking into account both perturbative
and nonperturbative effects, we use the method of vacuum correlators to derive
the Dirac equation (rigorously for the Coulomb interaction and heuristically
for the confining potential) for a system consisting of a light quark and heavy
antiquark. As a result the confining potential is a Lorentz scalar, and the
Coulomb part the fourth component of a 4-vector. The energy spectrum of the
Dirac equation is considered for these potentials. Numerical calculations of
energy eigenvalues $E=E_{n\kappa}$ are performed, and some exact solutions of
the Dirac equation in the case $E=0$ are found. An effective-potential method
convenient for qualitative study of the solutions of the Dirac equation is
developed. The connection with experimental spectra of $D$- and $B$-mesons is
briefly discussed.
