We present a first-principles theoretical study of the atomic geometry and electronics states of the InP(1 1 1)A surface under In- and P-rich conditions. The In-rich surface, characterised by an In vacancy per unit (2 x 2) cell, obeys the electron counting rule (ECR) and is semiconducting. Under P-rich conditions we have considered two surface reconstructions: (2 x 2) with 3/4 monolayer (ML) P coverage and (root 3 x root 3) with 1 ML coverage. In complete agreement with a recent experimental work by Li et al., it is found that the (root 3 x root 3) reconstruction is more stable than the (2 x 2) reconstruction. However, the (root 3 x root 3) reconstruction has a metallic band structure and thus does not satisfy the ECR. The stability of this reconstruction is explained to arise from a competition between the ECR and a significant elastic deformation in the surface region. We confirm the suggestion by,Li et al. that this surface can be passivated both chemically as well as electronically with 1/4 ML coverage of hydrogen. (c) 2006 Elsevier B.V. All rights reserved.