Prediction of Ground State Structures and Robust Weyl Fermionic States in MnRhP

Topological metals are a new class of materials that
feature Fermionic
quasiparticles with the presence of non-trivial band crossings near
the Fermi level. In this work, we focus on establishing crystal structure
ground states and the corresponding topological properties of MnRhP.
Under ambient pressure and low temperatures, we find that an orthorhombic
oP12 polymorph is favored over the known hexagonal hP9 phase. Pressures
above 15 GPa stabilize tetragonal (tP6′), hexagonal (hP9′),
and orthorhombic (oP12′) phases with inverted population of
metal sites. While oP12′ has the lowest enthalpy, we show that
hP9′ is more consistent with the previous X-ray diffraction
data collected at 60 GPa. Our analysis of hP9 and oP12 topological
properties reveals the existence of nodal lines around the Γ-point
that are gapped out when spin–orbit coupling effects are included
and transform into Weyl nodes with opposite chirality near the Fermi
level. The calculated large values of the anomalous Hall conductivity
in hP9, oP12, and tP6′ and the Z2 topological invariant in the non-magnetic hP9′ can be used
to verify the predicted non-trivial robust topological features of
MnRhP under ambient and high pressures.