Structural, electronic, and magnetic properties of a- and b-MnAs: LDA and GGA investigations

Yu-Jun Zhao, W. T. Geng, and A. J. Freeman 

Department of Physics & Astronomy, Northwestern University, Evanston, Illinois 60208

B. Delley 

Paul Scherrer Institute, WHGA/123, CH-5232 Villigen PSI, Switzerland

 ~Received 6 April 2001; revised manuscript received 27 November 2001; published 12 February 2002!

Abstract:

Zinc-blende (a-) and NiAs-type (b-) MnAs are investigated with a combined first-principles linearized argumented plane wave and DMol3 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 a-MnAs is 10% smaller than that of GaAs, which is in contradiction to the well-accepted fact that the lattice volume of Ga12xMnxAs increases with x. In contrast, the GGA predicts a reasonable lattice volume for a-MnAs. The ferromagnetic a-MnAs is shown to be a metal at a55.7 Å, and to undergo a transition to a half-metallic phase when it expands to a.5.8 Å due to the decreased bandwidth. Further, the calculated cohesive energy of b-MnAs is nearly 0.87 eV greater than that of a-MnAs, which provides theoretical support for the instability of a-MnAs.


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