  In the framework of the quark delocalization color screening model, we
investigate tetraquarks composed of $us\bar{d}\bar{b}$ and $ud\bar{s}\bar{b}$
in two structures: meson-meson structure and diquark-antidiquark structure.
Neither bound state nor resonance state is found in the system composed of
$us\bar{d}\bar{b}$. The reported $X(5568)$ cannot be explained as a molecular
state or a diquark-antidiquark resonance of $us\bar{d}\bar{b}$ in present
calculation. However, two bound states of the diquark-antidiquark structure are
obtained in the tetraquarks system composed of $ud\bar{s}\bar{b}$: an $IJ=00$
state with the mass of $5701$ MeV, and an $IJ=01$ state with the mass of $5756$
MeV, which maybe the partners of $X(5568)$ states. Our results indicate that
the diquark-antidiquark configuration would be a good choice for the
tetraquarks $ud\bar{s}\bar{b}$ with quantum numbers $IJ=00$ and $IJ=01$. The
tetraquarks composed of $ud\bar{s}\bar{b}$ is more possible to form bound
states than the one composed of $us\bar{d}\bar{b}$. These bound states are
worth investigating in future experiments.
