  Recent experiments on switching antiferromagnetic domains by electric current
pulses have attracted a lot of attention to spin-orbit torques in
antiferromagnets. In this work, we employ the tight-binding model solver,
kwant, to compute spin-orbit torques in a two-dimensional antiferromagnet on a
honeycomb lattice with strong spin-orbit interaction of Rashba type. Our model
combines spin-orbit interaction, local s-d-like exchange, and scattering of
conduction electrons on on-site disorder potential to provide a microscopic
mechanism for angular momentum relaxation. We consider two versions of the
model: one with preserved and one with broken sublattice symmetry. A
non-equilibrium staggered polarization, that is responsible for the so-called
Neel spin-orbit torque, is shown to vanish identically in the symmetric model
but may become finite if sublattice symmetry is broken. Similarly, anti-damping
spin-orbit torques vanish in the symmetric model but become finite and
anisotropic in a model with broken sublattice symmetry. As expected,
anti-damping torques also reveal a sizable dependence on impurity
concentration. Our numerical analysis also confirms symmetry classification of
spin-orbit torques and strong torque anisotropy due to in-plane confinement of
electron momenta.
