  Using first-principles electronic structure calculations based on density
functional theory (DFT), we investigate the structural, electronic and magnetic
properties of the layered ternary manganese tellurides: AMnTe2 (A = K, Rb, and
Cs). Calculations are accomplished within the full-potential linearized
augmented plane wave (FP-LAPW) using the generalized gradient approximation GGA
formalism for the exchange correlation term. We have treated all ferromagnetic,
antiferromagnetic and non-magnetic phases and found that the ferromagnetic is
the ground-state for all studied compounds. Moreover, all three compounds under
study are half-metals with a total spin magnetic per formula unit of 4 mu_B
which is mainly localized at the Mn atoms. We express for these compounds a new
version of the Slater-Pauling rule and discuss in detail the origin of the
minority-spin gap. Finally, we have also calculated some other relevant
quantities such as the bulk modulus B, the pressure derivative B', the virtual
semiconducting gap Eg, and the half-metallic gap E_HM.
