  Recently, the topological nature of an antiferromagnet YbMnBi2 has been
controversial. YbMnBi2 is regarded as a candidate of Type-II Weyl semimetals
with magnetic moments of Mn atoms canting about 10{\deg} in some studies but as
a Dirac semimetal without canting in others. By means of systematical density
functional theory calculations, we show the perfect YbMnBi2 bulk has a
collinear antiferromagnetic ordering and, naturally, it is a Dirac semimetal.
Considering the vital role of magnetic moment canting in generating the Type-II
Weyl state, we artificially cant the magnetic moments of Mn atoms and find that
YbMnBi2 enters into the Type-II Weyl state from about 2{\deg}. Inspired by this
and taking into account the possible defects in experiments, we suggest that Bi
vacancies in Mn-Bi-Mn bonds, which produce sizable Dzyaloshinskii-Moriya
interactions and thereby cant the magnetic moments of Mn atoms, can tune the
topological nature of YbMnBi2 from Dirac semimetals to Type-II Weyl semimetals.
Our work unveils the possible underlying mechanism for the Type-II Weyl state
in YbMnBi2, providing insights into the Weyl state in other magnetic
topological materials.
