  Computationally modeling the behavior of wavelength-sized non-spherical
particles in optical tweezers can give insight into the existence and stability
of trapping equilibria as well as the optical manipulation of such particles
more broadly. Here, we report Brownian dynamics simulations of non-spherical
particles that account for detailed optical, hydrodynamic, and thermal
interactions. We use a $T$-matrix formalism to calculate the optical forces and
torques exerted by focused laser beams on clusters of wavelength-sized spheres,
and we incorporate detailed diffusion tensors that capture the anisotropic
Brownian motion of the clusters. For two-sphere clusters whose size is
comparable to or larger than the wavelength, we observe photokinetic effects in
elliptically-polarized beams. We also demonstrate that multiple trapping
equilibria exist for a highly asymmetric chiral cluster of seven spheres. Our
simulations may lead to practical suggestions for optical trapping and
manipulation as well as a deeper understanding of the underlying physics.
