On the calculations of the static electronic dipole (hyper)polarizability for the free and spatially confined H⁻

The quality of the static electronic dipole (hyper)polarizabilities (α and γ) calculated using the coupled cluster with singles and doubles (CCSD) method and various basis sets for the isolated hydrogen anion (H⁻) was verified against highly accurate results obtained within the variation-perturbation scheme with the optimized explicitly correlated Gaussian functions. Moreover, the influence of spatial confinement on α and γ of H⁻ was analyzed. The effect of confinement (orbital compression) was modeled by the spherically symmetric harmonic oscillator potential. Our results demonstrate that in order to obtain the value of α with a relative error less than 10% and correct order of magnitude of γ for the unconfined H⁻ at the CCSD level of theory, at least triply augmented correlation consistent basis set (t-aug-cc-pVXZ, X = D,T,Q,5,6) has to be used. Furthermore, it was found that the spatial confinement significantly affects α and γ of H⁻.