The radiative torque (RAT) mechanism is the most promising way of explaining observed polarization arising from aligned grains. We explore the efficiency of the grain alignment by an anisotropic radiation flow for an extensive ensemble of grain shapes. We calculate the distribution of the ratios of the amplitudes of the two major components of the RATs, that is an essential parameter that enters the theory of RAT alignment in Lazarian & Hoang (2007, LH07). While this distribution is different for different classes of grain shapes that we considered, the most probable values of the parameter are centered in the range of q max ∼ 0.5 − 1.5. The functional form from RATs calculated is in good agreement with the analytical model (AMO). We find that the RAT efficiency scales as (λ/a) −3 for λ a as previously found in LH07. This increases the power of predictions obtained with the RAT theory. We also confirm that superparamagnetic inclusions are necessary in achieving high degrees of alignment, and constrain the parameter space describing the requirements for achieving these alignment degrees.

We study the efficiency of grain alignment by radiative torques (RATs) for an ensemble of irregular grains. The grains are modeled as ensembles of oblate and prolate spheroids, deformed as Gaussian random ellipsoids, and their scattering interactions are solved using numerically exact methods. We define the fraction of the grains that both rotate fast and demonstrate perfect alignment with grain long axes perpendicular to the magnetic field. We quantify a factor related to the efficacy of alignment and show that it is related to a factor of the analytical model of the RAT theory. For the interstellar radiation field, our results indicate that the degree of RAT alignment can reach ∼0.5, which may be sufficient to explain observations even if grains do not have magnetic inclusions.

We establish a theoretical framework for solving the equations of motion for an arbitrarily shaped, inhomogeneous dust particle in the presence of radiation pressure. The repeated scattering problem involved is solved using a state‐of‐the‐art volume integral equation‐based T‐matrix method. A Fortran implementation of the framework is used to solve the explicit time evolution of a homogeneous irregular sample geometry. The results are shown to be consistent with rigid body dynamics, between integrators, and comparable with predictions from an alignment efficiency potential map. Also, we demonstrate the explicit effect of single‐particle dynamics to observed polarization using the obtained orientational results.