Shell model description of weakly bound nuclei

Structure of weakly bound/unbound nuclei close to particle drip lines is different from that around the valley of beta stability. This short review discusses the recent progress in modeling these exotic nuclei using an open quantum system formalism. The generic features of effective interactions in loosely bound systems are studied both in the analytically soluble model and in the realistic shell model in the complex k-plane (the so-called Gamow Shell Model) which uses a complex Berggren ensemble representing bound single-particle states, single-particle resonances, and non-resonant scattering states. In this formalism, we shall discuss the spectra of lithium isotopes and spin-orbit effects in unbound He-5,He-7 nuclei.