Cluster dynamics and single-particle correlation are simultaneously treated for the description of the ground state of 12C. The recent development of the antisymmetrized quasicluster model (AQCM) makes it possible to generate j j -coupling shell-model wave functions from α cluster models. The cluster dynamics and the competition with the j j -coupling shell-model structure can be estimated rather easily. In the present study, we further include the effect of single-particle excitation; the mixing of the two-particle-two-hole excited states is considered. The single-particle excitation is not always taken into account in the standard cluster model analyses, and the two-particle-two-hole states are found to strongly contribute to the lowering of the ground state owing to the pairing-like correlations. By extending AQCM, all of the basis states are prepared on the same footing, and they are superposed based on the framework of the generator coordinate method (GCM).