  We perform a coupled-channel study of the possible deuteron-like molecules
with two heavy flavor quarks, including the systems of $D^{(*)}D^{(*)}$ with
double charm, $\bar{B}^{(*)}\bar{B}^{(*)}$ with double bottom and
$D^{(*)}\bar{B}^{(*)}$ with both charm and bottom, within the
one-boson-exchange model. In our study, we take into account the S-D mixing
which plays an important role in the formation of the loosely bound deuteron,
and particularly, the coupled-channel effect in the flavor space. According to
our calculation, the states $D^{(*)}D^{(*)}[I(J^P)=0(1^+)]$ and
$(D^{(*)}D^{(*)})_s[J^P=1^+]$ with double charm, the states
$\bar{B}^{(*)}\bar{B}^{(*)}[I(J^P)=0(1^+),0(2^+),1(0^+),1(1^+),1(2^+)]$,
$(\bar{B}^{(*)}\bar{B}^{(*)})_s[J^P=0^+,1^+,2^+]$ and
$(\bar{B}^{(*)}\bar{B}^{(*)})_{ss}[J^P=0^+,1^+,2^+]$ with double bottom, and
the states $D^{(*)}\bar{B}^{(*)}[I(J^P)=0(0^+),0(1^+)]$ and
$(D^{(*)}\bar{B}^{(*)})_s[J^P=0^+,1^+]$ with both charm and bottom are good
molecule candidates. However, the existence of the states
$D^{(*)}D^{(*)}[I(J^P)=0(2^+)]$ with double charm and
$D^{(*)}\bar{B}^{(*)}[I(J^P)=1(1^+)]$ with both charm and bottom is ruled out.
