1. Centre for Computational Science, Department of Chemistry, University College LondonLondon WC1H 0AJ, UK
2. Centre for Virology, Windeyer Institute of Medical Science, University College LondonLondon W1T 4JF, UK
3. The National Hospital for Neurology and Neurosurgery, Queen's SquareLondon WC1N 3BG, UK