  Electronic, magnetic, and transport properties of the antiferromagnetic (AFM)
CuMnAs alloy with tetragonal structure, promising for the AFM spintronics, are
studied from first principles using the Vienna ab-initio simulation package. We
investigate the site-occupation of sublattices and the lattice parameters of
three competing phases. We analyze the factors that determine which of the
three conceivable structures will prevail. We then estimate formation energies
of possible defects for the experimentally prepared lattice structure. Mn$_{\rm
Cu}$- and Cu$_{\rm Mn}$-antisites as well as Mn$\leftrightarrow$Cu swaps and
vacancies on Mn or Cu sublattices were identified as possible candidates for
defects in CuMnAs. We find that the interactions of the growing thin film with
the substrate and with vacuum as well as the electron correlations are
important for the phase stability while the effect of defects is weak. In the
next step, using the tight-binding linear muffin-tin orbital method for the
experimental structure, we estimate transport properties for systems containing
defects with low formation energies. Finally, we determine the exchange
interactions and estimate the N\'eel temperature of the AFM-CuMnAs alloy using
the Monte Carlo approach. A good agreement of the calculated resistivity and
N\'eel temperature with experimental data makes possible to draw conclusions
concerning the competing phases.
