  In this work, we evaluate the energy spectra of baryons which consist of two
heavy and one light quarks in the MIT bag model. The two heavy quarks
constitute a heavy scalar or axial vector diquark. Concretely, we calculate the
spectra of $|q(QQ')>_{1/2}$ and $|q(QQ')>_{3/2}$ where $Q$ and $Q'$ stand for
$b$ and/or $c$ quarks. Especially, for $|q(bc)>_{1/2}$ there can be a mixing
between $|q(bc)_0>_{1/2}$ and $|q(bc)_1>_{1/2}$ where the subscripts 0 and 1
refer to the spin state of the diquark (bc), the mixing is not calculable in
the framework of quantum mechanics (QM) as the potential model is employed, but
can be evaluated by the quantum field theory (QFT). Our numerical results
indicate that the mixing is sizeable
