1University of Oxford, UK
2University of Cambridge, UK
We present ONETEP, a density functional program for parallel computers whose computational cost scales linearly with the number of atoms and the number of processors. ONETEP is based on our reformulation of the plane wave pseudopotential method which exploits the electronic localisation that is inherent in systems with a non-vanishing band gap. We summarise the theoretical developments that enable the direct optimisation of strictly localised quantities expressed in terms of a delocalised plane wave basis. These same localised quantities lead us to a physical way of distributing work among many processors to allow calculations to be performed efficiently on parallel supercomputers. We show with examples that ONETEP achieves excellent speed-ups with increasing numbers of processors and confirm that the time taken by ONETEP as a function of increasing number of atoms for a given number of processors is indeed linear. What distinguishes our approach is that the localisation is achieved in a controlled and mathematically consistent manner so that ONETEP obtains the same accuracy as conventional cubic-scaling plane ers fast and stable convergence. We expect that calculations with onetep have the potential to provide quantitative theoretical predictions for problems involving thousands of atoms such as those often encountered in nanoscience and biophysics.