  The magnetic properties, electronic band structure and Fermi surfaces of the
hexagonal Cr2GeC system have been studied by means of both generalized gradient
approximation (GGA) and the +U corrected method (GGA+U). The effective U value
has been computed within the augmented plane-wave theoretical scheme by
following the constrained density functional theory formalism of Anisimov et
al. [1991 Phys. Rev. B 45, 7570]. On the basis of our GGA+U calculations, a
compensated anti-ferromagnetic spin ordering of Cr atoms has been found to be
the ground state solution for this material, where a Ge-mediated super-exchange
coupling is responsible for an opposite spin distribution between the ABA
stacked in-plane Cr-C networks. Structural properties have also been tested and
found to be in good agreement with the available experimental data. Topological
analysis of Fermi surfaces have been used to qualitatively address the
electronic transport properties of Cr2GeC and found an important asymmetrical
carrier-type distribution within the hexagonal crystal lattice. We conclude
that an appropriate description of the strongly correlated Cr-d electrons is an
essential issue for interpreting the material properties of this unusual
Cr-based MAX-phase.
