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Abstract

We report the results of a theoretical study of the electronic and structural properties of the hexagonal beryllium nitride, using first principle pseudopotential plane wave (PP-PW) as well as full potential linearized augmented plane wave (FP-LAPW) methods within density functional theory. In the case of PP-PW we generated the pseudopotential by the highly optimized Qc-tuning method and used the local density approximation and generalized gradient approximation (GGA) for the exchange-correlation potential. We applied pressure on the unit cell by the Wentzcovitch and traditional methods. In the FP-LAPW approach only the GGA was used for the exchange-correlation potential. Our calculated values for structural properties, based on both approaches are in reasonable agreement with experimental and other theoretical (Hartree Fock) results. By applying the above two approaches and also the Tight Binding Linear Muffin Thin Orbital method, the ground state Kohn–Sham eigenvalues were calculated. The energy bands in three cases were similar and except for the energy gap values they were in good agreement with other theoretical results. Various versions of GGA functionals are usually obtained by optimizing the exchange correlation energy EXC rather than the corresponding potential VXC. As these functionals are not able to simultaneously reproduce EXC and VXC, hence they cannot obtain an accurate value for the band gap which mainly depends on the potential. Engel and Vosko (Phys. Rev. B 47 (1993) 13164) have proposed an alternate form of GGA which is based on optimizing VXC instead of the integral quantity EXC. We used this functional to calculate the band gap and the result seems to be more reasonable. Finally the total and partial densities of states were calculated for each atom.