1. Materials Modelling Centre, University of Limpopo, Private Bag x1106 , Sovenga 0727, South Africa
2. School of Physical Sciences, University of Kent , Canterbury CT2 7NZ, UK
3. The Center for High Performance Computing, Council for Scientific and Industrial Research, Meiring Naude Street , Brummeria 0001, South Africa
4. Hans Merensky Holdings, Saxonworld , Johannesburg 2132, South Africa
5. Department of Chemistry, University College London, 20 Gordon Street , London WC1H 0AJ, UK
6. School of Chemistry, Cardiff University, Park Place , Cardiff CF10 3AT, UK