A Comparative Study of the Influence of the Local Density Approximation and the Generalized Gradient Approximation on th
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A Comparative Study of the Influence of the Local Density Approximation and the Generalized Gradient Approximation on the Calculated Properties of the III-Nitride (110) Surfaces H. W. Leite Alves and J. L. A. Alves DCNAT-FUNREI, CP 110, 36.300-000, São João del –Rei MG, Brazil. R. A. Nogueira DF-ICEx-UFMG, CP 702, 30.161-970, Belo Horizonte MG, Brazil. J. R. Leite DFMM-IF-USP, CP 66.318, 05.389-970, São Paulo SP, Brazil. ABSTRACT We present a systematic theoretical study of several III-nitride (110) surfaces based on accurate parameter-free, self-consistent total energy and force calculations using the density functional theory, the local density approximation (LDA), as parametrized by Perdew and Zunger, and the generalized gradient approximation (GGA), as proposed by Perdew, Burke, and Ernzerhof, for the exchange-correlation term; we use the Full Potential Linear Augmented Plane Wave (FPLAPW) approach (WIEN-97 code) associated with the slab supercell model to simulate the (110) surface. We studied BN, AlN, GaN, InN and compared the theoretical results as related to the use of the LDA and the GGA. We conclude that although the results for both approximations are similar, differences in structural parameters may be as large as 10%. INTRODUCTION The knowledge of the atomic and electronic structures of surfaces are of essential role in understanding the behavior of microelectronics devices. In particular the optoeletronics based on III-nitrides and their alloys is an area of intensive experimental and theoretical study nowadays, due to their promising applications in the whole range of the visible spectrum as well as in the ultraviolet range. Theoretical calculations of these materials have been available for the last five years, including semi-empirical quantum calculations, Hartree-Fock cluster calculations and calculations based on the density-functional theory. In spite of this large number of studies, several issues remain unresolved. Let us consider, for instance, the surface (110) of the cubic phase of the GaN compound. This surface is considered to be important for applications in optoelectronics. Nevertheless its experimental study is scarce (probably due to the difficulties in growing the samples) and, to our knowledge, no low energy electron diffraction (LEED) has been reported for this surface yet. At ambient conditions the III- nitrides crystallize in the hexagonal wurtzite phase with the exception of BN. However, thin films of BN, GaN, InN, and perhaps, AlN may be grown epitaxially in the zinc-blende structure. Up to now all cubic films have been grown along [001], what may explain why no LEED data are available.The theoretical studies have conducted to some controversy about the magnitude of the surface tilt angle [1]. In preliminary studies [2] we have reported theoretical parameters for the III-nitrides (110) surfaces as obtained using the generalized gradient approximation [3-5] within the density functional theory [6]. The generalized gradient approximations (GGA’s) to the exchange correlation (XC) e
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