Elimination of basis set superposition error in linear-scaling density-functional calculations with local orbitals optimised in situ

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.