Novel recipe for double-hybrid density functional computations of linear and nonlinear polarizabilities of molecules and nanoclusters.

Double-hybrid (DH) density functionals are now among the most applied methods for quantum chemical calculations within density functional theory (DFT). In this work, a new DH density functional is developed for linear and nonlinear optical properties of molecules and hydrogen-bonded nanoclusters. The proposed functional, denominated as PBEDH-P (-P stands for polarizability), is based on Perdew-Burke-Ernzerhof (PBE) exchange and correlation functionals and includes 68% Hartree-Fock exchange and 31% correlation from second-order Møller-Plesset perturbation theory (MP2). From the obtained results, PBEDH-P is shown to be accurate for the calculations of hyperpolarizability, isotropic and anisotropic polarizabilities, and dipole moment of molecules and hydrogen-bonded nanoclusters of H2O (neutral, protonated, and deprotonated), NH3, HF, and binary mixtures of HF-H2O. This novel DH functional not only reveals a considerable improvement in comparison to the recently proposed parameter-free and parametrized DHs but also seems to be superior to the MP2 method in some cases. Moreover, we find that using only contributions of electron pairs with opposite spin for the perturbative part within scaled opposite-spin scheme does not represent a great improvement over PBEDH-P. On the whole, our study nominates PBEDH-P as a promising model for the calculations of electric response properties, where the DH density functionals again come into play and further evidence of the quality of these approximations are highlighted.