  The optical properties of nanoparticles can be substantially affected by
their assembly in compact aggregates. This is a common situation notably for
nanoparticles synthesised and self-assembled into rigid clusters in colloidal
form, where they may be further characterised or used in spectroscopic
applications. The theoretical description of such experiments generally
requires averaging the optical response over all possible cluster orientations,
as they randomly orient themselves over the course of a measurement. This
averaging is often done numerically by simulating the optical response for
several directions of incidence, using a spherical cubature method. The
simulation time increases with the number of directions and can become
prohibitive, yet few studies have examined the trade-off between averaging
accuracy and computational cost. We benchmark seven commonly-used spherical
cubature methods for both far-field and near-field optical responses for a few
paradigmatic cluster geometries: dimers of nanospheres and of nanorods, and a
helix. The relative error is rigorously evaluated in comparison to analytical
results obtained with the superposition T-matrix method. Accurate orientation
averaging is especially important for quantities relating to optical activity,
the differential response to left and right circularly polarised light, and our
example calculations include in particular far-field circular dichroism and
near-field local degree of optical chirality.
