2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/190916The excited states of Be-12, Be-14 and B-15 have been studied with a method of antisymmetrized molecular dynamics. In the predicted excited states we find novel molecule-like structures with very exotic clusters such as 6He+8He in Be-14 and 6He+9Li in B-15. The origin of the He-6 cluster development in the very neutron-rich nuclei is understood by the new-type correlation among 4 neutrons and 2 protons. In this paper we also present our recent challenge to study $sd$-shell nuclei. Shape coexistence problems in Ar-36 and Ca-40 are discussed.10 pages, 5 figures. The proceedings of Yukawa International Seminar 2001 on "Physics of Unstable Nuclei". To appear in Prog. Theor. PhysNuclear Theorytext