Ab initio calculations, based on pseudopotentials and density functional theory, have been performed to investigate the effect of hydrogenation on the atomic geometries and the energetics of substitutional boron on the generic Si(001)-(1 x 2) surface. For a single B atom substitution corresponding to 0.5 ML coverage, we have considered two different sites: (i) the mixed Si-B dimer structure and (ii) boron substituting for the second-layer Si to form Si-B back-bond structure, which is energetically more favorable than the mixed Si-B dimer by 0.1 eV/dimer. However, when both of these cases are passivated by hydrogen atoms, the situation is reversed and the Si-B backbond case becomes 0.1 eV/dimer higher in energy than the mixed Si-B dimer case. For the B incorporation corresponding to 1ML coverage, among the substitutional cases, 100% interdiffusion into the third layer of Si and 50% interdiffusion into the second layer of Si are energetically similar and more favorable than the other cases that are considered. However, when the surface is passivated with hydrogen, the B atoms energetically prefer to stay at the third layer of the Si substrate. (c) 2007 Elsevier B.V.. All rights reserved.