  We have studied the interactions between two heavy mesons
($D^{(*)}$-$D^{(*)}$, $\bar D^{(*)}$-$\bar D^{(*)}$, $B^{(*)}$-$B^{(*)}$, or
$\bar B^{(*)}$-$\bar B^{(*)}$) within heavy meson chiral effective field theory
and investigated possible molecular states. The effective potentials are
obtained with Weinberg's scheme up to one-loop level. At the leading order,
four body contact interactions and one pion exchange contributions are
considered. In addition to two pion exchange diagrams, we include the one-loop
chiral corrections to contact terms and one pion exchange diagrams at the
next-to-leading order. The effective potentials both in momentum space and
coordinate space are investigated and discussed extensively. The possible
molecular states are also studied and the binding energies are provided by
solving the Schrodinger equation. The results will be helpful for the
experimental search for the doubly-heavy molecular states.
