Cluster states in stable and unstable nuclei

In this contribution, I will discuss two topics related to the clustering of atomic nuclei. The first is dual character of the ground state. Recently, it was pointed out that the ground states of atomic nuclei have dual character of shell and cluster implying that both of the single-particle excitation and cluster excitation occur as the fundamental excitation modes. The isoscalar monopole and dipole transitions are regarded as the triggers to induce the cluster excitation. By referring the Hartree-Fock and antisymmetrized molecular dynamics calculations, the dual character and those transitions are explained. The second is the linear-chain state of $^{16}{\rm C}$ in which the linearly aligned 3$\alpha$ particles are sustained by the valence neutrons. The rather convincing evidences for this exotic state are very recently reported by several experiments. Here, I introduce a couple of theoretical analysis and predictions.