We critically review the ΛΛ dynamics by examining Λ - Λ and Λ-nucleon phenomenological potentials in the study of the bound state properties of double-Λ hypernuclei _ΛΛ⁶He, _ΛΛ¹⁰Be, _ΛΛ¹⁴C, _ΛΛ¹⁸O, _ΛΛ²²Ne, _ΛΛ²⁶Mg, _ΛΛ³⁰Si, _ΛΛ³⁴S, _ΛΛ³⁸Ar, _ΛΛ⁴²Ca, _ΛΛ⁴⁶Ti, _ΛΛ⁵⁰Cr, _ΛΛ⁵⁴Fe, _ΛΛ⁵⁸Ni, _ΛΛ⁶²Zn, _ΛΛ⁶⁶Ge, _ΛΛ⁷⁰Se, _ΛΛ⁷⁴Kr, _ΛΛ⁷⁸Sr, _ΛΛ⁸²Zr, _ΛΛ⁸⁶Mo, _ΛΛ⁹⁰Ru, _ΛΛ⁹⁴Pd, _ΛΛ⁹⁸Cd, _ΛΛ¹⁰²Sn in the frame work of (core+Λ+Λ) three body model. An effective ΛN potential is obtained by folding the phenomenological ΛN potential into the density distribution of the core nuclei. The former two cases (i.e. _ΛΛ⁶He and _ΛΛ¹⁰Be) are revisited to justify the correctness of the present potential model. Assuming the same potential model we predicted some of the structural properties of heavier doubly Λ-hypernuclei. The hyperspherical harmonics expansion method, which is an essentially exact method has been employed for the three body system. A convergence in binding energy up to 0.15% for K_max=20 has been achieved. In our calculation we have made no approximation in restricting the allowed l-values of the interacting pairs.

Hyperspherical harmonics expansion method is applied to a three-body model of two neutron halo nuclei. Convergence of the expansion has been ensured. A repulsive part is introduced in the interaction between the core and the extra-core neutron, to simulate Pauli principle. Two neutron separation energy, r.m.s. radii, correlation factor and probability density distributions have been calculated for ⁶He. It is found that the convergence of the two neutron separation energy is relatively slow, while other quantities reach convergence quickly.