  For a two-sublattice antiferromagnet the Lagrangian is constructed taking
into account Berry phase whose form is matched to the quantum-mechanical
Heisenberg Hamiltonian. Tunnel effects are analyzed taking into account the
crystallographic symmetry and possible types of the Dzyaloshinskii-Moriya
interaction. It is shown that, when the real magnetic symmetry and the
Dzyaloshinskii-Moriya interaction are taken into consideration, the effects of
a destructive instanton interference and the suppression of macroscopic quantum
tunneling can play an essential role. It also may lead to a periodic dependence
of the ground-state level splitting on the Dzyaloshinskii-Moriya interaction
constant; the magnitude of this splitting is calculated.
