Structural, electronic, and magnetic properties of α- and β-MnAs:: LDA and GGA investigations -: art. no. 113202

Zinc-blende (alpha-) and NiAs-type (beta-) MnAs are investigated with a combined first-principles linearized argumented plane wave and DMol(3) study within both the local density approximation (LDA) and the generalized gradient approximation (GGA). First-principles calculations within the GGA predict the lattice volume for b- MnAs much better than LDA (which underestimates it by 15%) compared with experiment. The LDA calculated equilibrium lattice volume of alpha-MnAs is 10% smaller than that of GaAs, which is in contradiction to the well-accepted fact that the lattice volume of Ga1-xMnxAs increases with x. In contrast, the GGA predicts a reasonable lattice volume for alpha-MnAs. The ferromagnetic alpha-MnAs is shown to be a metal at a=5.7 Angstrom, and to undergo a transition to a half-metallic phase when it expands to a>5.8 Angstrom due to the decreased bandwidth. Further, the calculated cohesive energy of beta-MnAs is nearly 0.87 eV greater than that of alpha-MnAs, which provides theoretical support for the instability of alpha-MnAs.