The role of generalised gradient approximation in structural and electronic properties of bulk and surface of beta-GaN and GaAs

Using the first-principles pseudopotential approach, we have performed calc ulations of the total energy, atomic structure and chemical bonding for bul k and surfaces of GaAs and cubic GaN to assess the role of the generalised gradient approximation for the exchange-correlation energy combined with th e non-linear core correction (NGGA). Our calculations show that the applica tion of NGGA does not produce significant changes in the structural paramet ers and the electronic band structure for bulk and for the non-polar (110) surface. However, the application of GGA is of considerable importance for the atomic and electronic structure of the polar (001) surface. (C) 1999 El sevier Science B.V. All rights reserved.