  We show by means of density functional calculations that CaMn$_{2}$Sb$_{2}$
is very close to a mean-field critical point known for the classical Heisenberg
model on the honeycomb lattice. Three entirely different long range ordered
magnetic phases become degenerate at this point: the Neel phase and two
different spiral phases. We speculate that the unusual physical properties of
this compound, observed in recent experiments, in particular the enigmatic
intermediate temperature phase, are due to this proximity.
