  The accurate computation of non-linear optical properties (NLOPs) in large
polymers requires accounting for electronic correlation effects with a
reasonable computational cost. The Random Phase Approximation (RPA) used in the
adiabatic connection fluctuation theorem is known to be a reliable and
cost-effective method to render electronic correlation effects when combined
with the density-fitting techniques and the integration over imaginary
frequencies. We explore the ability of the RPA energy expression to predict
NLOPs by evaluating RPA electronic energies in the presence of finite electric
fields to obtain (using the finite difference method) static polarizabilities
and hyper-polarizabilities. We show that RPA based on hybrid functional
self-consistent field calculations yields as accurate NLOPs as the best-tuned
double-hybrid functionals developed today, with the additional advantage that
RPA avoids any system-specific adjustment.
