Interplay Between Bond Stretching and Confinement Effects on the (non)linear Electrical Response of HeH+

In this study, the impact of spatial confinement on the linear and nonlinear electrical properties of the helium hydride ion ( HeH^+ ) is investigated using highly accurate ab initio CISD method with an extensive daug-cc-pV6Z basis set. The confinement environment is modeled by a cylindrical harmonic oscillator (HO) potential, and the variation of the dipole moment and (hyper)polarizabilities on the internuclear distance is analyzed along the entire dissociation coordinate. Our findings demonstrate that the spatial restriction leads to a systematic reduction in all investigated electrical properties, a phenomenon primarily attributed to the widening of the HOMO–LUMO energy gap and electronic density compression.