We report an ab initio pseudopotential calculation for the atomic and electronic structure of Bi/GaAs(001)-α2(2 × 4). Three structural models with Bi coverages of Θ = 1/4 are considered, containing one Bi dimer or two Bi-As mixed dimers. According to our calculations for this coverage, the atomic model of the Bi/GaAs(001)-(2 × 4) reconstruction is similar to the α2 structure of the clean GaAs(001)-(2 × 4) surface in which the top As dimer is replaced by a Bi dimer. This result is in agreement with the most recent scanning tunneling microscopy work. © 2008 IOP Publishing Ltd.