1Theory of Condensed Matter group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Ave, Cambridge CB3 0HE, UK
2Physical & Theoretical Chemistry Laboratory, South Parks Road, University of Oxford, Oxford OX1 3QZ, UK
3Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge MA, USA
Basis set superposition error (BSSE) in density-functional calculations occurs when the extended Kohn-Sham orbitals are expanded in localised basis sets, but is absent when a plane-wave basis is used. Elimination of BSSE is essential for the accurate description of intermolecular forces. Linear-scaling methods are formulated in terms of local orbitals, making plane-waves an inappropriate choice of basis. In this work the BSSE in linear-scaling methods is studied in the context of hydrogen bonds. In particular it is shown that BSSE is eliminated by optimizing the local orbitals in situ using a systematic basis set equivalent to a set of plane-waves.