We present calculated dielectric function epsilon(omega) and linear optical absorption alpha(omega) of the cubic and hexagonal structures of BN, AIN, GaN, and InN, employing an all-electron linearized augmented plane wave method within the local density approximation (LDA) plus quasi-particle (QP) correction. We show that this LDA+QP approach yields accurate high-frequency dielectric constant Moreover, by employing a modelled electron-optical phonon interaction we calculate the static dielectric function epsilon(0). (c) 2007 Elsevier B.V. All rights reserved.