  We have studied the hard magnetic properties of the low-temperature phase of
MnBi with first principle calculations based on the density functional theory.
The calculations have been carried out on two distinct unit cell configurations
MnBi and BiMn with the element in the unit cell origin named first. Our results
show that these configurations are not equivalent and that MnBi describes the
system better near T = 0K and the BiMn configuration describes the system
better for T > 300K. The magnetic moments of both configurations agree well
with experimental measurements considering both spin and orbital contributions.
At high temperatures the magneto-crystalline anisotropy energy increases with
increasing unit cell volume and reaches a maximum of 2:3MJ=m3 and a c=a ratio
of 1:375.
