Critical stability and quantum phase transition of screened two‐electron system

The ground state energy and structural properties of a model two‐electron system ( Zee ), bound via screened Coulomb interaction with nuclear charge Z , have been studied under the variational framework. Hylleraas type basis has been adopted for explicit incorporation of the electron–electron correlation. Critical nuclear charges ( Z c ) of Zee system have been reported for different screening parameters ( μ ). Expectation values of different structural properties have been estimated to predict the internal structure of the Zee system. The variation of the structural properties with respect to Z for different μ reveals the signature of quantum phase transition (QPT) in the vicinity of Z c . Moreover, the nature of variation of these properties with respect to Z in case of bare Coulomb or free system ( μ = 0) is completely opposite to those of screened system ( μ  ≠ 0). Radial two‐particle density (TPD) confirms the symmetry breaking of the electronic structure and therefore QPT in the vicinity of Z c .