Stimulated by the recent observation of the exotic X(5568) state by D0
Collaboration, we study the four-quark system usbĖdĖ with quantum
numbers JP=0+ in the framework of chiral quark model. Two structures,
diquark-antidiquark and meson-meson, with all possible color configurations are
investigated by using Gaussian expansion method. The results show that energies
of the tetraquark states with diquark-antiquark structure are too high to the
candidate of X(5568), and no molecular structure can be formed in our
calculations. The calculation is also extended to the four-quark system
uscĖdĖ and the same results as that of usbĖdĖ are
obtained.Comment: 5 pages, 1 figur