Possible hadronic molecular states composed of S-wave heavy-light mesons

We perform a systematical study of possible molecular states composed of the S wave heavy light mesons, where the S-D mixing and eta-eta' mixing are explicitly included. Our calculation indicates that the observed X(3872) could be a loosely shallow molecular state composed of D (D) over bar* + h.c, while neither Z(c)(3900)/Z(c)(4020) nor Z(b)(1.0610)/Z(b)(10650) is supported to be a molecule. Some observed possible molecular states are predicted, which could be searched for by further experimental measurements.